If the 1989 is like my 1980, besides a gasket you will need some dedicated copper-plated hex nuts for the stud connection to the manifold. The dealer sells them--don't know whether anyone else does.

You can only tighten these one time, so make sure you have everything lined up and the gasket snug. Each nut has an integral "lock washer" with copper ribs on its face. The ribs flatten out when you tighten the nut. If you try to reuse the nuts or even retighten new ones, the ribs get squished out to where they don't bind when everything gets real hot, and your header pipe keeps coming loose. Happened to me several times.

I suppose you could use the old nuts to test tighten. Hmmmm. The gasket may also be a one-time-use. Don't recall--it's been a long time. (Which is good, in a way--once you get it back together right you won't have to mess with it for another ten years.)

Good luck.

Doug Harvey