[AZKen]

I agree with the swap to 63-66. The 60-62 and the 67-72 frames could be lots more work that you think. The hard part is finding a 63-66 4x4 frame. The easy part, in any idea, is fabbing a motor mount/tranny mount. The T-221 xfer case and the closed knuckles are headaches. Consider an option to upgrade to NP205 and open knuckles. But now we are talking a bigger project than swapping 65 body to 63-66 4x4 frame.
The 60-62 GMC frames are different, I believe, than 63-66. Your info says you have a 63 GMC 1/2 ton? Before you damage too many trucks, maybe sell the 2wd and buy a 4wd. That will take about the same amount of time and money as a swap..... or less.