Confusion indeed!
I have two different mopar catalogues with the same P4876908 part number.
the only difference being pin height.
Crate engine catalog states this block is 10:1 comp with cast heads (587 or 596)
The 2005 mp catalogue says 9.1:1 with the same heads.
The only difference being pin height.
My calculations tell me Im in the 9’s for compression due to the pistons at top being in the hole a c hair.
About .024 in the hole.
Maybe the Cummins built here in Canader had lower compression?
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I get about 8.9 to 1 compression with your piston and bore dimensions, a Fel Pro 4.18 bore and .048 compressed thickness head gasket, and a guess of 72cc for 596 casting head.

If you do nothing but change to a Cometic head gasket with a 4.06 bore and .027 compressed thickness you are around 9.37 to 1 compression.

Then of course as the chamber gets smaller the numbers go up a little from there. Make sure you measure your chamber volume to get better numbers.