Large rpm drop

I ran your numbers and got 10.7 static CR, so you are in the right ballpark for that. Your DCR is 8.4-8.6 so that explains the detonation issues. A larger cam by 1-2 steps would lower that and would make tuning easier.

Go back to post #20 and re-read what AJ has explained. You have too much initial timing and that is messing you up. The old idea of adjusting idle timing for maximum idle RPM goes out the window when you get to the higher dynamic compression ratios like you have. The cylinder's torque pulses get much 'peakier' than for a low compression engine, and that spins the crank faster when it is unloaded. But when you load it, the average crank torque is not all that much higher and the RPM's load way down.

And with your 'all-in' being so low (1800-2000 RPM), you may be getting more advance pulled in at that idle of 1100-1200 RPM. Having your mechanical advance come in so fast is also contributing to you detonation issues.

Our 340 at 10.0 SCR and 8.0 DCR has 15 degrees initial timing. No idle drop problems and all was good for the transition once the secondary transfer slot was closed down a bit.

And as said, if drawing off the mains at idle, you will see fuel dripping down from the boosters (and even hear it if your ears are still good).