This only happened 2 twice in a 5 mile test drive and never from a standstill. It happens not always after coasting, make a turn, feather the throttle, carb stumble at 5-7 mph, pop/backfire through the carb and then takes off.
Erratic fuel pressure and float level may be the problem.
Ignition is the FBO system provided by MRL with FBo ignition box and ballast resistor bypass jumper installed.
Check your firewall connections are clean.
The distributor curve was done at MRL. Total was 36* at 3000rpm with the vacuum advance disconnected. I don't have the dyno sheet with me but I believe the initial is 18*
FBO always has a curve sheet and specifies if hooked to manifold or ported vacuum. IMO if your at 18* you want to run manifold vacuum to bump up idle timing.
The guy working on finishing it says timing is good and is ASE certified with over 30+ years experience and works on older classics. He is old school. I had a '71 Demon with 318 Rochester that acted the same way with a carb that went away with a Carter. I found out later that was a Chrysler TSB on that carb in '71.
Rear gear was stated up in the thread 3.23 and tires 235/60 R14 rear front 215/70 R14