Could you give us a little more information here? I'm assuming that your 1989 is a 350 and the heads are from something smaller?

If you have some part or casting numbers I'm sure there's help out here.

It's not just a matter of "will it fit" as most small block Chevy parts interchange however: there are some combinations that will perform very poorly, i.e., 350 heads on a 305 can end up with 6:1 compression ratio. Great starter speed but no performance at all...

Set some numbers..
Glenn