Absolutely use them if you have them. On a big block chevy, 2 of the cylinders, on each side, so, 4 total, have an inherant flaw, with a wide span between the 2 upper head bolts. The other 2 cylinders, have a bolt in between there. It is VERY common, to push the gaket out, on the 4 cylinders without that extra head bolt. I have 2 540 3300 intercooled Whipple Charged big block chevy's to re-do, as the oil is milky, and, they had very bad blow by. Turned out, the block and heads had a horrible 85B finished decks, that, combined with regular fel-pro gaskets, without those bolts, all 4 of the cylinders where the bolts were missing, were pusherd out there, leaking compression, and water from the coolent hole right by there. You could see the saw tooth pattern, indented into the fire ring, and, it wasn;t completely sealing very well. They were pretty poochy too, only like 730 hp, with the blowers. I have a naturaly aspirated marine 540 combo that makes that much power. So, picking these up by 100+hp, without being more racical, should be easy.
So, I will be re-block truing the blocks, on the 10-V with cbn, for a smooth finish, re-cutting the heads, and using Fel-Pro MLS gaskets. Also, when I un bolted the heads, the head bolts were fairly losse. I don;t think the heads were re-tqed after the initial running. Which I will also do. I always do that. Especially with the composition Fel-Pro's, and aluminumn heads, even though, they say you don;t need to.
I am rambling again, but, definately use them. Like was mentioned some lock tight for sure.
Frank
Advanced Performance
www.get-ap.com