Ignition primary for 12v conversion

[PGBuick]

I am converting my ‘36 to 12v neg ground as part of an engine swap ( now a ‘48 59 AB). The engine came with a 12v Powermaster one wire alternator and a Powermaster starter. The pic attached is the resistor unit found under the dash of the original ‘36 6v system. I presume this is a voltage reducer for the ‘36 coil, not really sure. I now have the ‘48 distributor and plan to use a ‘60’s vintage 12v gm coil I had on the shelf. What voltage does the coil need while running? And what value ballast resistor will achieve that? Also, with the stock ‘48 points distributor, should I include a full voltage resistor bypass in the start circuit, or is this unnecessary?
Thank you,
Pat