[99 to Life]

There are several ways to distinguish the Advance designs (AD) aka 1947-55 1st series trucks. There are 1/2, 3/4 and 1 tons (noted by hood emblems as 3100, 3600 and 3800 I believe) also frames and beds are a tell tale.
Their wheelbases are as follows
116 in
125.25 in
137 in

However the factory truck wheels are actually offset 2" in the rear, so that is why the Reg Cab "longbed s-10" works so well.

S-10 wheel bases are as follows (all have been used in some way or another)
Regular cab short box - 108.3" (AD bed gets shortened)
Regular cab long box - 117.9" (most common used frame little mods)
Extended cab short box -122.9" (AD bed stays same, s-10 frame shortened)
(All of this is assuming you are using the AD short bed truck)

Body mounts will never line up. You have to make custom ones, it isn't too big a deal. S-10 route is a great way to go. When you get into the 4x4 stuff, that opens all kinds of problems, not saying it hasn't been done, but 4x4 just complicates things quite more.