B&M Converter is bad

Quit worrying about total timing at this point and get the idle timing and carb settings right.

New carb? Are the floats set properly?

Timing FIRST, then adjust the carb mix screws. Get it warmed up. Advance idle timing 2* at a time, shut off, restart. Do this until you find point that starter drags like the battery is dead and back off timing 2*. Keep 800 idle RPM same when doing this, it should pick up RPM as you advance timing. Lock it down and see where the initial is at that point. Reset the idle speed 800rpm, then hit your mix screws, max idle vacuum with them in the most. See if the car still drops a bunch in gear. If it does, put a light on it and see if the number you saw when locking it down is different. If it is, then the distributor is tossing in mechanical advance and that MUST be corrected, stiffer spring(s).

How you end up with two different advance numbers when revving it up is beyond me. That should be consistent.

Is there a large port opening on the back of that carb that may be unplugged?

Do one thing at a time because it looks like you get overwhelmed by the big picture.