Jeepers creepers...I reckon I was right. On several accounts.
First off, using grease to drive those brake pistons out made the biggest pig mess you can imagine. In fact, WORSE than I imagined! There is grease and greasy rags everywhere. But I did manage to get all 8 pistons out of the bores...
I'm sure you know already that once you start removing stuff you just can't stop. And you also know that you wind up with parts stacked everywhere, over, under, in-between and upside down. Your only hope is to keep the ball in play and don't stop. Subscribed!
If yours is a stock '69 the CR is 10:1
Here's the thing; the RN12YC plug is a resistor plug (denoted by the "R"). If your plug wires are also resistor (carbon core) wires they can cause misfire at mid to upper range RPMs, especially in higher gears with higher compression pistons. Don't ask how...
Here are a couple questions for you...
1) What is your compression ratio?
2) Solid (copper core) or resistor plug wires?
3) Solid or resistor plugs?
4) Are you running MSD?