spotts performance makes and sells brackets that bolt to the front and back of the heak and the header then bolts to them for the holes the heads dont have. www. spottsperformance.com. check it out. although i do agree that you should not have any problem sealing using good gaskets. i always wipe a thin coat of high temp silicone on each side of the gasket anyway to assure less chance of an exhaust leak.
nothing at all against the new gen firebirds and camaros but its nice to see there is still interest in the first gen ( and the best gen) firebirds.