Compression leaking to valvetrain

Always nice to get updates on these things; tnx!. Sounds like the heads may have been tad warped and those thin head gaskets did not like it. Once they warp at all, sealing up gets pretty 'iffy'.

The standard Felpro's (8553PT) are somewhere around .050" thick, versus the .028" thick of the Mr Gasket 1121G. So there is a need for the lifters to take up the extra slack in the pushrods. The heads were milled but we don't know how much; assuming it was less than .022" (and it usually is well under .010" to just clean and true up the head surfaces), then you just might have a just-too-short pushrod right now. Or just a poor lifter.

I'd run the engine for a minute and then shut off ( to pump oil into all the lifters), take off the valve covers, and, for the lifters/rockers that are fully closed, see if there is any slack or softness in the lifter/pushrod side on each and every valve. You'll have to turn the engine over some to get all of the valves in the closed position, a few at a time.

While you are in there, re-torque the head bolts. I don't care if they are 'Permatorque' types.... it is good practice to do so.