The later rings were thinner to reduce friction. The power difference from the CR change will be about 5% since your dropping the compression from 8.7 to 7 or about 5 to 7 HP.

Many re-builder pistons are decked and drop the CR by another 1/2 point. The idea is to account for milled cylinder heads. Just a warning that you may end up with a real CR of 6.5 to 1.

If the rods were overloaded, the upper bearings should be worse. If the damage is the same, it might be from air in the oil or cavitation.

That would explain why the crank was still OK.

87 Turbo Intercooled Raider, roller cam, torsen rear diff, LSD front diff, lockup auto with modified converter, V6 brakes, low transfer case gears...