Don,
I have a few questions that may help you get a better response.
Do you have the original frame or just the cab and bed?
Why are you wanting to swap frames?
What size truck do you have? LB or SB?
What is your intended use?
I put my 51 cab on a 78 frame. I would expect you to run into the same problems that I did. The frame steps down for the 78 floor pans this is the same in the 71. I had to build up the frame for my cab supports. I used the old frame for the donor metal and cut it to the contour of the drop. This worked out pretty good. I also had to build radiator mounts, which was not a real big issue. The worst part of it all is the wheels do stick outside the fenders a little and the entire cab sits up higher over ther wheels than the original. I yor truck is a 1/2 ton the wide and high stance is probably not what you are looking for. Even with a 3/4 ton or 1 ton it gets into that iffy zone. Drop spindles will help but you will have to be careful not to get into you fenders. Rodney Godwins 49 in the gallery has dropped spindle but he modified the wheel opening.
I suggest you research as much as you can in the gallery and do a search because this topic has been discussed several times.
