Drive shaft thoughts

I know a guy that is selling drive shafts from dodge 3/4 and 1 tons, same from c word and f word hd trucks, I believe most are aluminum.
I was wondering if it would be okay- wize to get 1 with 1350 u-joints & have it cut down, welded & balanced. I believe they are mostly 4 & 5 inch diameter.
2nd question can a stock floor pan fit a 5 inch.
3rd question will they handle mid 600 hp and torque, 2 step & foot brake