Great - I have a 1989.
I think you should have a 350ci carb engine?
Mine is a LO5 (350 TBI).
The y-pipe from the 92-93 9C1 is larger than in 89, so is a cheap upgrade. Not sure if its a bolt-on for your car, but it works for 89. the exhaust on these cars is pretty bad, so anything to open it up is good.
Another site to check is third-gen.org - f-body site, sicne the cars share a lot of driveline parts, there is good reference.
As for suspension, a lot of it is the same as the newish (94-96?) Impala SS. So springs, shocks, etc work for the most part. I plan to do the PST bushings, already have new shocks, keeping the 89 9C1 springs (I think they are the stiffest, or very close to stiffest, from GM). Some of the F-body front swaybars bolt up - do a search to find the years. Also, the SS 17x8 alloy wheels fit and aren't too expensive if you want shiny rims.
Have fun with it.