Timing Question

I also have wondered about the harmonic balancer and timing marks slipped. When you bring the number one piston up to top dead center the balancer shows it's zero for zero. My idle is right at 750 RPM. I am using the ported vacuum on the carburetor. When I switched from pertronics to Mopar electronic ignition with the orange box this is when most of my problems started. I pulled another distributor out of the junkyard to use for the car for my electronic ignition conversion as the old distributor was worn at the shaft and the one that I got from the junkyard had no slop in it at all.