WIth the help of a chain-type tailpipe cutter rented from Autozone, a length of 2.5" OD 409 stainless 16 gauge pipe donated by a new pal I made at the local muffler shop, a 1/2" deep socket (and an Accuseal clamp to put it back together securely
) I was able to completely remove the stock cat and answer all my questions:
1) The DP to cat flange gasket turned out to be reuseable.
2) The opening of the stock cat had no obstruction to the insertion of 2.5" length of 2.5" OD pipe.
3) AccuSeal exhaust clamps are the greatest invention of all time.
I'm now all prepped for my exhaust mod in the near future