Actually you're in luck as I'm in the middle of doing pretty much the same thing. I cut the entire floor pan off a 91 2wd club cab and I'm grafting it onto the bottom of my 934wd club cab. They are almost exactly the same. The only differences are the hole for the transfer case shifter, and 2 little bolts that hold the heat shield for the exhaust on the passenger side.the mounts and everything line up perfectly. But a word of advice.... Spend the extra money on a 2 inch body lift. It gives you alot of extra space to work. And it gives you a good stance.
if you have more questions please feel free to ask me as I'm in the middle of doing this on my truck so I can give ya alot of help

 

On a side note after reading your post again, you can't use a 2nd gen frame, the only thing that will line up is the bed mounts, you can fit a 2nd gen bed on a 1st gen frame and vice versa. But the cab mounts, core support mounts etc won't line up the same. It can be done but you're going to be building custom mounts on the frame, drilling new holes for bushings etc. You may be better off fixing the bad spots on your own frame.
i had to fix several spots on my frame. I had to cut out some bad spots and weld in New steel. I also added some support at the rear of the frame where the hitch mounts.
If you need any of the cross member that run under the bed I have some extras I'd be willing to sell