Well for what it's worth probably nothing lol.
I had a convo with Cometic people and they told me unless BOTH the head and block are machined flat they wouldn't recommend using their gasket.

here's some post from a Racing related forum....


I put Cometic gaskets on a 540 Chevy blown gas Jet Boat engine and had no problems. no o-rings, no leaks. 8.25 static compression PSI A blower 25 lbs boost @ 80% overdrive. 1544 hp @ 7200 rpm. This was the first set I have used. We even took them off once during assembly & once during the dyno session. They are reusable. I like the way they seal & don't leak. Jet Boats are very hard to seal with o-rings & copper gaskets. I use a wet segmented stone surface grinder to deck the block & surface the heads with a very fine finish. My customer loves them because he has battled water leaks with most of his engines. I will use them again.

With any MLS gasket, surface finish is the #1 priority. What you can get away with on a composite gasket WILL NOT WORK with a steel gasket.

If you want to read the rest of the input or comments... http://speedtalk.com//forum/viewtopi...18dd3f73d6af8f