New and looking for Frame help

[7TDEUCE]

Hello, new to the website, I have a 72 which was a long bed converted to a short bed. I think that it may not have been correctly modified, as when you look from behind and line up the back part of the bed with the bottom of the window, the right side is higher by about 1-2 inches. I have tried adding some spacers to even it up, but its still off a bit and me being OCD, drives me nuts...lol. So I have been thinking of searching for an original SWB frame or donor... and wonder if all the 67-72 frames (C10, K10, stepside vs fleet etc) are basically the same/interchangeable... or would other years require some modifications? I'm sure this questions has been addressed here many times, but I couldnt find a thread on it. Any help or guidance is greatly appreciated! Thank you!!