You use 26 degrees of advance at the crankshaft. But is it 13 or really 12.5? It sounds like the good Mopar Performance distributor. It is better to time to 35 degrees at 2,500 rpm and let the initial fall where it may. It may be partially advanced at your idle speed. Are you sure TDC is at "0" on your balancer? If not you can "time it by ear" look for RRR's method.