The only frame that's going to fit under a 57 RIGHT is a TF, 55.2 to 59 frame, or something custom made.
GM ran the same chassis on their trucks from 73-87. I have seen those adapted under a TF, never quite fit right. Those frames have curves the trucks aren't built for. There are wheelbase issues to boot. I can't remember for sure, the later one is longer or shorter by a few inches.
I measured a friend's 97 standard cab swb 1/2 ton against my own 57 I had at the time and wheelbase and track width looked good, but the frame was much wider in the center and had far more curves than a TF.
A TF frame is basically a ladder frame, virtually straight. GM went away from that in 1960 when independent suspension first arrived.
What are your goals for your truck, how are you going to use it, how do you want it to ride, and at what height do you want it to ride?
Devin
