Single Exhaust pipe size?

[Davids71C20]

I have a few thoughts rolling around about my exhaust and I could use some input.

I'm getting closer to my truck being on the road again. I dropped a crate 350 in from a 6 and so I need new exhaust. I got the engine off of a 1981 c10 with single exhaust, looks like 2.25 inch. But that exhaust was for a 305...matters?

I'm also wondering what pipe sizes a 1971 C20 350 would have had on it new. Was it the same diameter as the inline 6?

What is the best size for a single exhaust for fuel economy. I know its a 3/4 ton with a 350 but I'm trying to squeeze what I can out of it. Also a dual exhaust would cost me twice ($1000) what a single would cost ($550) and I'm on a tight budget. Auto work in Alaska is more expensive.

Another idea was to cut and weld an exhaust from the 1981 system and a few pipes from an 1985. I would need to buy/borrow a welder though.

Kind of a loaded thread.