Choosing the right carb for my car (340 4-speed)

Figure out what's going on with your timing. Something isn't right... verify the TDC timing mark on your balancer with a piston stop and go from there.

A decent starting baseline for an aggressive cam is about 20* initial. Sometimes really big cams and lower compression engine need more timing to run at idle. Your current reading are REALLY out of bounds for a total timing number.

Check for vacuum leaks.