Looks like a paint roller, well sorta :?
Stick within your budget and open it up as best you can.
Dont they make a high flow combo cat/res, dynomax? Bill?

go up to 2.5 on that piping since you are replaceing alot of the parts anyway.

I still need mandrel bent pipe though i'm not going to buy crush bent crap. And thats alot more welding.
I might be spending alot this summer but i still got a tight budget with everything i'm trying to do. If i do the 2.5" then i'm sacrificing a paint job or being able to mill the heads or money for gaskets/fluids.