2-1/2" to stock downpipe exhuast question


I'd rather be waterskiing
Here's the situation. Exhaust is all completely stock (including gutted cat). The original Y-pipe split a seam and is now unusable.

I would like to run a single 2-1/2" pipe to a new cross-mounted muffler that has a single 2-1/2" in and two 2-1/4" outs. I only have money to do this is steps, so can't afford a down-pipe and bigger cat right now. Any ideas on how to tie the 2-1/2" pipe to the current cat without having a bunch of rework later when I do upgrade the down-pipe and cat?