The heads were bolted onto the block with Milodon's dead-soft, solid copper head gaskets. Their .040-inch thickness specs give us a quench clearance (piston-to-head) of .050 inch. A sealant is required around all the coolant holes with the copper gaskets. Milodon recommends silicon, but we opted for Permetex Hylomar non-hardening sealant, since we expected to swap heads. Based on our expe-rience, Hylomar seals like a vault. We'll let you know how it worked for this purpose. We torqued down with Milodon's high-tensile head bolts-rather than with studs-for easier head swapping on the dyno.