I probably will never get the answer but doesn't hurt to ask:

Does anyone know the diameter sizes of

1. Stock catalytic input and output?
2. Stock Y pipe input is 2" and output is 2.5"?
3. Stock Y-pipe-back exhaust (after the Y-pipe) is 2.5"?

I'm assuming the stock catalytic's output is 2" since it needs to be the same size as the stock Y-pipe, if the above measurement is correct.

Anyone who has their old parts laying around, please let me know. It's very important. Thanks a lot