I did the same. I always felt like under the window bars was very under built on a lot of trucks I have seen. Got these extensive c pillar areas and then not much going on under the window bars.Looks good. On my Tacoma I ran down tubes behind the dash from where your windshield bars intersect to the bar going across for the seat mounts. Actually fit in there pretty good and I think you could keep your dash like it is but the radio and heat would be in the way if your keeping them.
I actually went from under the window bars to the seat tube as posted right above, built my center console around that. I also went from under the window bars down slightly through the firewall. They were hard tubes to make and doubt would work with hvac, but if those were there I would say you can leave that tube out as there would be a "tie down" point slightly further toward the cab.Nothing that goes straight down but they go through the cowl
You would probably be okay without it, but I would try to sneak it in if possible.
Not sure what you have going on where the outer engine cage tubes meet the a pillars, but I would put a hefty gusset in there. Mine is a 7" piece of tube, 45 degree angle on both sides heading toward engine cage. I then plated over that whole triangle. When I was caging mine I kept reading about trucks cracking there and it makes sense. Lots of flex there. Adding that tube you are talking about would also keep that flex down.
Fab work looks great dude!
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