Tear it down and let them measure it, IN FRONT of you. They could have easily given it too much clearance (don't forget that cast or forged pistons determine that amount) and ask "what gives??" Could be a bad hone job too; Again, did a professional bore and hone this??
Your DC is not the issue, many guys don't run them until they snap the kicker off.
We have 25 year old OEM pistons still on the 1st bore running well out there.
I've seen mixed up rings, too much end gap rings and upside down rings.
I've also seen oil rings stuck or staggered wrong.
That 86 motor does not like 12:1, 10.5 with a pipe will be just fine.......
All our government does is distract us while they steal from us, misspend our tax $ and ruin our country