everything exhaust wise will bolt up like the original b18a so no need for bigger exhaust, the mounting on the 94+ integra's is different anyways.
if your b18a1 trans is still good I'd say leave it in, but if you want to get the hydro tranny in you're gonna need a hydro mount and hydro conversion kit in order to run everything properly. You're also gonna need an obd0 to obd1 conversion harness, Idk if they make obd0 to obd2, obd2 distributor,you can get away with not converting over and just slappin the b18b, thats the set up in my car and everything works like it should. some of the wiring is different for the temp sensors I think,(can't remember off hand) but a quick search will help you with that.