Can't help you much on the exhaust. I use a round (not bullet-style) Dynomax racing muffler (3 inch inlet and outlet), but I typically hit about 100db at the track. Never been over 103, but I have gotten close on a bad day - cold and low overcast. To meet 95db, you'd need something closer to a street system, smaller pipe and more restriction, or maybe run a pre-silencer of some type. I think there has been a thread on meeting much lower db requirements that a few tracks have, so you might find some ideas there (too lazy to try to look it up myself .) A Supertrap after a regular muffler might do the trick for an autocross, but don't trust my limited knowledge on that one.

I'll probably be at the April CMP SARRC event, so I'll look you up there.