1949 3600 to 3100 conversion questions

[49'3600]

Hi all,
I am new to this forum and forums in general so i apologize in advance for lack of knowledge... I recently purchased a 49' 3600 here in Tucson, AZ. No significant rust, original motor and trans, straight cab, but still a total project. It currently has a flatbed that looks to be a made-to-fit bolt on type deal. I have found a bed off of a 3100 nearby. My end goal is to make this truck have the look of 3100 in a sense. Then get to the mustang 2 front suspension, 383 stroker, ford 9 inch ect... Most of which i already have. I have been told the s-10 frame is the way to go but i would rather not go that route. This frame is in excellent shape and i am not afraid to cut, weld, box, ect... My first question on this build is at the rear. From what i have read, the difference between the 3600 and 3100 is 9.75 inches in frame length / wheel base?? Also is the 3600 frame is more narrow at rear as the leafs are mounted on the side of frame rail rather then underneath??? If the rear is more narrow does that mean the front is as well??? I have little knowledge of these trucks but i am itching to learn. Thank you all in advance for taking the time to read this. Any advice is greatly appreciated. I am pumped about this cool old chev and looking forward to hearing from you all!