my '86 2bbl roller cam motor was .055" in the hole. the cop motors use the same pistons. with the thin Mr. Gasket head gasket, and assuming my magnums were 64cc (I didn't have time to measure them) I should be at 9:1 exactly. I had the motor torn down to the bare block, and in hind sight I wish I would have had it decked .040, that would've given me .043" quench and 9.9:1 compression.

your '88 cop car block, if it's a 4bbl, should be a roller block, but flat tappet motor. I'd try get the entire valvetrain (cam, lifters, lifter "dogbones", spider retainer, pushrods, & rockers) from a magnum donor. & get the roller cam reground

one caveat with the magnum heads, you'll most likely have to rework your alternator bracket, and you may have to space your accessory drive out .2". I had to, to clear the alternator in my 5th ave. the accessory holes are in the same place, but are all on the same plane, vs. the LA accessory holes, which are on 2 planes offset ~.7".