I wouldn't read too much into what parts are there or not. Especially since it's been rebuilt.(and it's a 40+ year old engine) The Merc 390 used the same parts as the Ford 390. Only thing different was the high comp 2 bbl motor in the Mercs, and then that was just the use of the 2 bbl intake in place of a 4 bbl. As for the comp ratio, you can look up the piston part numbers and find that part out by doing the math with the comp height. The side seals on the rear main are supposed to have the pins.