I always thought it was the older body style 83-88 S10 single cab long box that was the desired one to swap? And preferably a 4x4.
But... your best bet is to go grab the dimensions of the existing chassis from the Shop Manual and then lay everything out on your new frame.
Or there's a wealth of info here:
http://www.jalopyjournal.com/forum/s...light=s10+swap