If it's a 2.5" exhaust system, using a 2.25" Xpipe puts additional restriction into the flow - it can be made to fit. I want to avoid this restriction.

Putting a 2.5" Xpipe on a 2.25" exhaust can be made to fit as well with no impact except looks.

Fitting the same size pipe on the exhaust ensures the best flow and it will be a cleaner looking fit. I'm sure you are right, I'm probably going to go out and measure to be sure... just lazy and avoiding laying on the ground in the cold.

I'm looking forward to getting it welded in soon.