I've got them on my 496. Fresh motor, so can't give much info yet. My last set of MLS's burned through between cyl. 4 & 6, cutting a gouge half as thick as my little finger into my iron heads. Have since upped the compression, so I wanted more protection for my new high dollar aluminum heads. I really like their design.
-Tanner
P.S. I believe Ken is using them also, so you might PM him about them. You will have to retorque these gaskets after first couple of heat cycles. Mine didn't back off, but others have had water leaks if they didn't retorque, as advised by the company.