The Dremel idea is interesting, but first look at the opening size of the exhaust manifolds. If those are also under 2.25", then spending time on the down pipe opening doesn't help much right there. I'd try to make it evenly sized throughout.
I was browsing for a next muffler for my work truck, knowing a 2.5" size would be good for that, 306 when I get that done. The mufflers I have to put in my good SUV(Black Coal I've named it), have 3" outlets and 2.5" inlets(2). The next size down is 2.25" twin inlets with a 2.5" outlet. That's good, as I was expecting, but pictures show they go into the identical muffler case, and cost almost $20 more. I'll save money and use what I have, adapt the pipes near the mufflers, and it'll work the same. The idea is, use what you have if it saves you time or money, and does basically the same thing. Merry Christmas,