the more I think about this engine the more I think any kind of performance ignition curve is a waste. your engine, in my opinion, is more efficient than a stocker with that high vacuum. I have a stock 440 I run around in and it's not as efficient as yours. i'd 'bet it's doing well over 20"hg vacuum at cruise speed; maybe 22-24",...? i'd try a curve very similar to the original mopar performance electronic distributors. I think that would be a good baseline and go from there. hopefully your not using a loose torque converter (if this is an automatic transmission) or low rear gears (numerically high).

try a 68x52 metering rod. something to keep in mind is the relationship between the engines high vacuum and the annular boosters. the high vacuum may be making the annular boosters over sensitive. i'm sure once the vacuum advance comes into play some of that carbon will be cleaned up. i'd take the FBO distributor apart and see what's in there.

This plug is not to cold
The mixture is to rich though, lean it down a little

Hi, thanks for answer. Im driving Ngk 6 now, the carb is one step leaner with 63-47 metering rod and the original 5hg orange feather,i have 18hg inch vacuum at idle. I get the FBOdistributor working properly now, its running better with that, no misses at idle and a rock steady timing mark, better with vacuum advance for the street. It looks rich, this big Mopar seems to not want so much fuel😃

Factory metering rod is .065x.052

If you are running .063x.047 metering rods with the factory jets .104

You are over 8% RICHER from stock

If you don’t want to dig into the carb to change the Primary Jet

Keep the factory .104 Primary Jet

First try

A .068x.057 Metering Rod and see how your plugs look and the car runs

10 minute job

I run the 7" Vacuum Metering Rod Springs Also