you might already have read up these trucks but in case you haven't here is a wikipedia thing. it explains a few differences that only the 54 and 55.1 will have. doing this will be cool but also make it a little harder to find parts.
https://en.m.wikipedia.org/wiki/Chev...Advance_Design
3600 is a 3/4 ton, correct? so not the big truck front end.
try to find an assembly manual. it will have frame dimensions, cab dimensions, where spot welds are located, all sorts of things that you can reference during take apart, repair, modification and assembly.