Ditto on the big cables and clean connections! My first project car back in the early 1960's was a 47 Mercury with a bunch of Dad's leftover dirt track racing parts on it including a set of Offenhauser finned aluminum cylinder heads. With the bore and stroke I chose, I had 11.25:1 compression. Making that thing start on 6 volts was a challenge. In addition to big battery cables and clean connections, be absolutely sure to keep it tuned well- - - -clean spark plugs, good points, correct dwell and timing, and good plug wires. Heavier than original wires in the primary ignition circuit from the battery cable at the starter, to the ammeter, ignition switch, and coil might also be a good idea. The coil needs to have a low-resistance voltage supply as well as the starter, because the load of the starter is going to drop the voltage available at the coil. You might also consider using a 12 volt starter switch, the one that has the side terminal on it, and bypass the long circuit I just described during starting with a piece of #12 wire directly from the starter switch to the coil + terminal. That would assure you're getting maximum voltage to the coil during cranking.
Jerry
