From everything I have read, here is what I would do, to give you the best chance of success:
1. Torque all of the bolts in sequence to your finish torque (80 ft-lbs. in your case). Do this in one step, without the head gaskets on the car.
2. Loosen all of the bolts and repeat the above procedure 5 times. The purpose of this is to "condition" the threads - remove all of the burrs, smooth-out the contact surfaces, etc. It takes forever, but it's worth it, as you will get more consistent bolt stretch when you make your final torque later on.
3. Remove the heads and install the head gaskets.
4. Use clean engine oil under the heads of the bolts. Others use moly lube, but you will need to torque to a lower value if you use moly. Apply thread sealer to the threads of all of the bolts. Install the bolts finger-tight into the heads.
5. Torque the bolts in sequence in the smallest steps you can stand. I would initially torque all of the bolts in sequence to 20 ft-lbs., then go around and increase the torque on each bolt in sequence in 10 ft-lb. increments, until you get to 80. The point of this is to duplicate the factory head bolt install procedure. In the factory, the head bolts were torqued all at the same time on a "multiple". You want to attempt to duplicate this on your heads as best you can.
Using the above prodcedure will take you all day, but I think it will give the best shot of the gaskets living.
You will get various opinions on whether or not you need to re-torque the bolts after a few heat cycles. From a gasket compression and bolt stretch point of view, it's probably a good thing. However, when you re-torque, you will disturb the thread sealant, which may be a bad thing. I guess my view is that GM did not re-torque head bolts on the original head gaskets, and we all know that the seal with the stock head gaskets is as good as it will get.
Another thing that you will hear is that you should torque-up the intake manifold to the heads BEFORE you finish torquing the head bolts. There is a thought that the intake manifold with pull the heads together when it's torqued and loosen the clamp load on the outsides of the head gaskets. If it were me, I would probably torque-up the intake manifold after I had all of the head bolts at 20 ft-lbs. Others may disagree.
Good Luck,
