I had the Powerglide with the 283ci V8 in my old 63 C10. I hated it. I ended up swapping in a TH400.
That swap required drilling out the rivets that held the rear support cross member in place, then relocating it a few inches rearward. I don't remember just how far back I had to go, it was over 35 years ago that I did that.
Good luck with your build though.
