The 73-87 wheelbase is longer for a shortbox (6') than the 55-59 frame. I am guessing that the longbox is the same. I am building a 4x4 from a 2wd 57 and I decided to use the frame and add drive train from a 79 shortbox 4x4. I used th original frame and I think it saves alot of work if you want a stock looking 4x4. just saying my 2 cents
