[PANAVIA]

MJH- My 410 has a C6ME block casting # and indeed came out of a Mercury Marauder.

the thing we have to watch is the piston pin height as the 410s used a piston .100" further up on the piston vs. the 390 piston. So if you use 410 pistons in a 390 crank, you will have LOOOOOWWWWWW compression , if you use 390 pistons with a 410-428 crank, you will need to check clearance to the cylinder heads or risk interference issues and diesel like compression ratios.

Ford used the 410 pistons in the 390 engines to make industrial FE applications (7.5:1)

--Steve