Dave, if the head has a porous area and if the leak is not that bad you could try the GM stop leak tabs that the dealerships sell. They are little tablets of organic matter that help seal cooling systems and they work fantastic. Gm came out with them for the porous aluminum heads on the newer cars that would leak slightly due to casting abnormalities. They help clot the system and really do work. They will not hurt the cooling system and you can put several tablets in at a time.. Just go to a Chevy/GM dealership and ask for the cooling system stop leak tablets and they should have them in stock.
If your problem is more severe I would pull the heads and check them out more carefully and do a proper repair... The problem is most probably in your heads I would guess. I am no "expert" though........
Hope this was of some help.....
Rich
