Help on 408 build

OP, please list the SCAT kit number so we can be sure we know what you are working with. And please re-run a cranking compression test before pulling the heads... I'd advise that you borrow a 2nd gauge and compare.

There is a lot of guessing going on, and the way forward will vary with what you actually have for static CR and dynamic CR. I am pretty solid at working out the numbers, and I am not seeing the high CR's that are being thrown about, with your use of J-heads, unless those heads have been milled a whole bunch or the cam timing is advanced a tooth. So something is not jiving between flat tops in open chambered J-heads, and your reported compression readings; I am getting low 10's for SCR and DCR's in the low 8's (at sea level), just running the first sets of numbers with typical J-head chambers and flat tops .012" below the deck.

The cranking compression numbers will be a good indicator of the DCR that you have right now. It may be as you say, but building a good baseline of data is what is needed right now.