Re: frame questions
The difference is where the spring hangers sit in relation to the frametails. If the hitch came off a 3/4 ton it should fit on a shortbox. 3/4 tons got 56" springs whereas halftons got 52". The difference between the shortbox frametail length and the 3/4 ton frametail length is probably very close.
Also, 2wds didn't get the frame support that goes between the lower part of the frame channel to the spring hanger. So if the hitch came off a 2wd it might not universally fit a 4x4. This is usually where the issue is at. This is especially true of Class V receivers which go forward of the spring hanger.
Moral of the story: measure it. Chances are you can modify it to fit anyway.