I just finished up a 68 440 Hp with the same pistons and heads as your 69. He had trouble with a stumble and pinging ever since the car was done and he was never able to get it right. I worked on the carb and realized it was more to it than carb problems. I got an FBO distributor and ignition. It has a 16 degree initial timing with 34 total now. I have to run 93 octane with booster to get it at that. Iron heads don’t help. I’m not sure if the exact CR but it’s not much over 9:1. It now has 12-14 inches of vacuum and runs better than it ever has. No stubble or clatter.