As far as the TT dial not breaking dial tone, swap tip & ring. Those old dial pads are polarity sensitive and won't work at all (or may make sickly sounds) when polarity is reversed. I'll have to look at a BSP for a 620 panel to figure out your ringing problem. Have you checked all the basics first? Ring gen is actually making 100+ volts at 30hz? Ring gen is making it from the power supply to the 620A2 panel? Interrupter starting when the line is ringing and interrupted ringing is making it to the panel?

620 panel BSP