Have someone spin the engine with the starter for 15 seconds with the ignition off while you monitor the battery voltage at the posts (not the cable terminals). While still cranking, the voltage should not drop below 4.5 volts. If it does, either recharge of replace the battery. Then do the same test with the ignition switch on while monitoring voltage at the coil + terminal with the coil center lead removed from the distributor cap. I solved a chronic "slow start" problem on a 1955 International pickup by repairing a loose, dirty connection at the ignition switch that was dropping the voltage available to the coil during cranking to 3.5 volts. Huge battery cables and clean, tight connections are an absolute must. I learned 6V electrical diagnosis and maintenance back in the early 1960's on a flathead Ford V8 with 11.25:1 compression ratio Offenhauser finned aluminum cylinder heads left over from one of my father's 1/4 mile round track dirt racers!
Jerry
