I have a 1973 620 that for the last couple weeks had been running progressively worse, stumbling and occasionally backfiring, and getting harder to start. Then, it wouldn't start at all. I've replaced plugs, cap, rotor and the primary? (frontside) condenser. I tested the coil and got spark from that side. I have been reading up some and know that it could be a ground in the dist. or points. I am by NO means a mechanic and at this point haven't a clue what I'm really looking for or how to troubleshoot further. Have points coming tomorrow and could use some help in getting this thing running again. Its dual points.