Difference btween a 2wd and 4wd frame, reason inside

[Novalicious]

Have a clean 64 gmc crewcab. Have some porterbuilt stuff. Want to stretch the frame and add trailing arms. What is major differences besides the lack of the kick in the rear section of the frame over the rear axle? Front section the same, just without the mounting holes? My 4x4 frame is PERFECT and for sale on here, just can't get rid of it, figured it might be easier to stretch this than cut the truck up while its together and running, 2wd. i'm building a 2wd.
It is a 61 Apachche std cab long bed frame.

Thanks