Help on 408 build
Were the head gaskets those out of a standard Felpro gasket kit? And when you say uncompressed, do you mean these are the head gaskets' thickness after you pulled them out? That WOULD be very close to the compressed thickness.
Did you measure the piston height below deck with a caliper or feeler gauges referenced to a straight edge across the deck, or with a dial indicator? Checking by eyeball is not adequately accurate....Not trying to make your life hard but you want good numbers to get you as close as you can get.
If you have that SCAT kit number please post it. With the piston numbers, it will be possible to crosscheck your piston height measurement.