Help an old man tune a new to me 340

Captainkirk said
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 I know. Just sayin'.

The guy I bought it from in Iowa got it from the original owner in Texas that built the engine. So, the guy I got it from didn't have all the info. I asked him what the compression ratio was when I bought it, and he wasn't sure, but thought 10:1. So that lines up with a stock 69. I should have said I wasn't sure and have not confirmed the compression ratio. The engine came to me with Bosch wr8dc+ plugs, I replaced with RN9YC and no change in problem. I changed to the RN12YC along with timing change and its better but still some rough. It's in the lower rpm range, 1600-1800. The plug wires are orange Mopar electronic suppression G.X. 1-00 AATH. You can see them in this picture.