Input
Need a bit more before the guys here who do rebuilds and frame swaps can give good info :
What is wrong (if anything) with the current frame ? .
What do you want to do with the finished truck ? .
These are *very* good trucks , the entire frame is much better than most current 1/2 tonners as it was made to work and work hard .
It's simple and cheap to upgrade to disc brakes and the handling is good now and gets better cheaply .
The bodies are the weak point as GM cheaped out and used low quality steel that was far too thin and then they did *zero* rust proofing as most trucks back then were worked to death and traded in in 4 ~ 6 years so who cared if it rusted away ? .
To make it a nice Hobby Truck all you needs do is rebuild it and add AC , PS & PB etc. , some really good gas shocks (Bilsteins , not silver KYB junk) and replace the rear trailing arms' bushings , maybe box them too .
Or , make it a show truck with air bags and modern suspension you can brag about but never use 1/10th of .
Your choice , figure it out and ask again the good folks here will happily he;p you to decide and then make it happen .