Welcome to the SCCoA. Where are you located? Besides hangin' out here, one of the best things you can do is locate anyone in your area that also owns one of these beasts and share info. Put your locale in your sig or sumthin' and someone will spot it and you might then discover a wealth of tech right down the street or across town from you.
As far as your question, you're headed in the right direction by doing sumthin' about the exhaust. Other things to consider with a "new" XR7/SC are normal things that can create headaches & gremlins.
Take a good hard look at your motor & trans mounts, the originals fail on a regular basis.
Make sure your radiator is up to snuff, ours have a bad habit of partially clogging and we never think about it until too late. Rodding is the best cure.
Do a little pre-maintenance on your MAF unit. The sensor can get dusty/coated and cause problems, use a little bit of Windex to wash it. NO rubbing, just rinse it.
Concerning MAF, start lookin' for a later model housing. Stock '89 is 55mm, grab a 70mm and install it.
Others will chime in with tips you can use, hopefully you'll be glad you got the car (pun intended
) and will enjoy it. Be sure to cruise the Tech section of this bbs, just scan down a couple of pages and make mental notes of what you see. Bookmark a few threads that peak your interest for future reference, be sure to print out what you want to keep handy.
Good luck, and again welcome to the SCCoA.
'bird