Is the combustion chamber diameter on the 243 heads larger than the cylinder bore of a 5.3? If so, I would definately get 5.7 gaskets, so you dont run the risk of the head gasket hanging out into your combustion chamber. Or just get L33 gaskets, since they came with 243/799s from factory.

No they are 5.3 heads (862 castings)

oops, I dont know what made me think that, lol. I would run 5.3 gaskets, but if they had combustion chamber work to unshroud the valves, it still wouldnt hurt to measure the combustion chamber diameter.

Thanks for the tip. They did clean up the chambers and the valves are 2.02/1.6 so it would be a good idea to measure.

I'd use ls9 head gaskets. $90.

Doubt he does that!
He's unsure of using ls1/6 gaskets with a bore size of 3.910 vs a ls9 gasket bore of 4.100

So it doesn't matter if the ls9 has a larger bore? This is what I'm confused about.

small block chevy 350 gaskets arent 4.00 bore they are larger and people have been using them without problems.