I can tell you that we have a set of Cometics sealing fine so far on a 340 with Edelbrocks with no particularly spec'd surfacing work on either head or block. Heads new as surfaced from Edelbrock, and block surfaced to be very flat at a local shop. But not a ton of miles on the engine. ARP head bolts, not studs. Carefully torqued down in steps. Heads off and back on once wiht the same Cometics. I only went to Cometics to tweak the quench/squish gap.
Attached is the best pix I have of that block's surfacing work; Maybe YR can look and comment on how smooth this surface is.
I never have asked what particular surface my local shop puts on here in VA; the owner has built lots and lots of race engines (8's, 6's and 4's) for the local track, so they may just know how to put on a (finer?) finish. IDK. I've had machine work done one my rally engines are about 4 different shops in VA, IN, and OH over the years, and never had a head gasket issue except 1, and rally cars see a lot of heat cycles (but probably not the same peak power levels in terms of HP per ci). The head was warped in that 1 case. Otherwise, all standard kit gaskets, Permatorques and composition types, even with 14-15 psi boost..... no issues as long as the parts are good and flat.
And yes the bolts/studs have to stretch a miniscule amount to take the pressure on each cylinder firing. But IMHO it is a matter of degree. If they stretch .00001", then probably not any issue. We're not running top fueler engines here. At what HP level, this become more of an issue is something I don't know the answer to.
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