1970 GMC K20 “Big Truck” - I’m back from the dead

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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
The overland community doesn’t seem to think this is cool, so after being inactive for who knows how long.... here goes nothing.

This is a story heavy build thread so if you don’t like reading... sorry about all the words. I will do my best to post things chronologically, I’ve been working on this truck for almost 4 years on and off so I’ll work my way up from the very beginning to current status.

History:
This was my dads truck back when I was a kid, he owned it until I was about 5-6 years old. It was a mild hotrod/work truck for him, but we’d go camping in it frequently while growing up, typically towing a jayco tent trailer. He had bought it with a damaged front clip (previous owner found the center divider on the freeway) so he swapped the front fenders so the body would be straight (hence the lack of paint on them). At some point he brought it down to Johnson Machine Service in Monrovia, CA. He had them rebuild the engine, small block 400, they did some mild head work on his iron heads, and he threw a weiand 144 on it. The suspension was nothing special, re-arched springs for a 4” lift (probably closer to 3”) dual ranchos up front. Had (and still has) a th350 that has been gone through and apparently shifts amazing, as my uncle says “it would bark second gear better than any car i ever owned”. At some point when I was very young, we were t-boned by a drunk driver behind the cab and the bed was swapped with the closest paint match you could find

You get the picture...

My dad sold it to a friend when the supercharger seized up one day and that family friend owned it for 16ish years and never ended up fixing it.

Fast forward to 2016.

I had built/modified a couple trucks and had no toy and asked my dad if Bob (our family friend) still had the truck, he said yeah, and to give him a call. A few short weeks later I went out to see the truck, it was rotting in his yard (luckily not too bad out in the desert) and asked how much he would sell it for. Since he knew it was our family truck from our childhood, he said “I’ll take the same price I gave your dad for it because I think you should have it”

$1000 later I was dragging the truck, which we had fondly called “Big Truck” as a child (because it was obviously huge at the time) onto a friends trailer and the rear down and cleaning of 16 years of dirt and dust started.

Here’s how it was when I was a kid...



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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
Tapatalk won’t let me post multiple pictures at the same time...

but anyways! The manifold had been off the engine for some unknown amount of time so the engine was junk and after a lot of back and forth with my old man. I decided I would put a small block 400 in it again. I had originally planned on doing a little 383 but he remembered the truck a certain way and was insistent, so I gave in.
After being unable to source a viable candidate to rebuild, I said F it, if we’re doing it, we’re doing it right, so I picked up an Edelbrock 400 block, and the spiral began.

side note - I picked up 34”x10.50 KO2s and procomp wheels since I had a good idea the truck would need them first thing just to roll it onto the trailer
 

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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
The original plan was to simply replace things such as bearings, shocks, seals and fluids and get the thing back in the road ASAP. Well once I started tearing into it it became one of those “well since this is apart I might as well change/replace this...” types of deals so as I tore into it the engine had already started snowballing.

I picked up a forged scar rotating assembly with H beam rods and custom blower pistons (making actual displacement 409ci) and with the help of a close friend, was able to source a brand new “old casing” weiand 144...

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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
Mind you all of this was extremely spread out over time for various reasons, so let’s say I’m about a year into this now. The engine is still just parts in boxes and I’ve gotten fully distracted with tearing this apart
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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
Now 12-18 months in, we’re painting the frame and the short block is getting assembled again by Johnson Machine Service. Little did I know, I would be moving again and the project would be put back on hold so I slammed it back together just so it wouldn’t be in pieces while I was gone...

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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
Pretty hard to remember the exact order of events, but I had moved up to the Bay Area for a much better job and left the truck down south.

during this time I started to parts pile. My mellow, highboy restomod rebuild plans had evolved even more. I found myself looking for bypass shocks, shopping for leaf springs and looking for just about any way to free up horsepower.

that said here’s what I had ordered:
- Crossover steering kit as well as front and rear leaf springs and shackle flip kit from off road designs
- MSD ignition
- Wilwood caliper kit for the front
- Reid racing knuckles
- 3.0x12” quad bypasses that I found brand new on race desert (will go more into detail later on this whole endeavor and what it takes to squeeze those things in a 67-72 gm truck)

then the fun of installing it all...
So much had been messed with on the truck previously that getting the correct seals, bearing etc was a major pain.

im missing a lot of bits and pieces so if you have any questions just ask, I’m sure I have photos somewhere of what I did with x-y-z

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UrbanAssaultVehicle

Senior Member
Mar 14, 2012
502
19
18
Chatsworth, CA
Alright, last post for the night. 2-2.5 years into the build....
The engine had totally gone out of control at this point and this is what we were at
- Edelbrock SBC 400: 4 bolt splayed mains, capable of being bored .160 over safely!
- Forged Scat rotating assembly (we went over this)
- Edelbrock victor jr 220cc heads for full hydraulic roller valve train
- custom ground cam from Clay Smith

Annndddd...
I sold the 144 because it was on the small side for my displacement and picked up a Blower shop 192 billet blower set up to do 8.5psi of boost on my current set up

Outside of the engine, things also went out of control, I started my own little side gig for all the fabrication stuff I do. Also picked up...

- hydroboost master cylinder set up
- built some shock towers
- installed the new leaf springs

and assembled the long block... my “not a prerunner” was starting to get all the right parts for one and I’ve described it as a retro runner. Basically I have taken factory ideas, but applied new technology and started building what I would imagine they would have built in the 70s to prerun Baja if they had the parts available that we do now...

also forgot to mention, i picked up some LaPaz HIDs, designed my shock towers for the front and I shoehorned a 42 gallon suburban tank behind the rear axle which I will also go into more detail on later or whenever it comes up again..

thats all for tonight! If you read this far, thanks for checking it out, will post more over the next few days

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