7.25 to 8.25 swap? /6 to 318 swap?

I have a 72 Swinger HT with a /6, 904, and 7.25 rear-end. My son has an 84 D150 Prospector with a 318, 727, and a 8.25 rear-end. He moved out and left the truck with me. It got me to thinking about cannibalization. I got to thinking about taking my drive-train out and putting his in the Swinger. But I'm not really all that likely too since both run good. (My drive-train is coming out anyway so I can slap the body on a rotisserie for work/paint.) Besides my moral dilemma of cannibalizing a perfectly good contraption, I started to wonder about all the retrofitting involved. I'm pretty sure I won't, but what would I be looking at if I did?

Would his 8.25 even fit in the Swinger? Is there any 8.25 that would bolt in, in place of the 7.25? What Make/ Model would I need to find as a donor? If there's not a direct bolt in, what would be the best suited 8.25 with minimal mods?

Would an 8.25 improve ANYTHING behind a /6? Or would I be wasting my time without putting in a 318? I'm no race-car driver, so I'm not hoping to blow anybody's doors off, but I'd like to be able to get up to a highway speed in the Swinger without people blowing MY doors off.

Thoughts? Suggestions? I have access to some decent pull-a-part yards and I'm not pressed for time.