Hi,
Your 89 head has 9mm injector bores were the injector nozzle comes through the deck surface. This area tends to crack from the bore to the valve seat much easier then the 1991. 5 and newer 7mm heads. Also in stock form, the 1st gen heads don't flow quite as good as the late 93 and newer heads. I believe in the range of 5 - 7% less.
The block, crank, rods and even the pistons are a good base for making big power.
Hope this helps.