Blaine...........The commonally used Delco 10-SI 12 volt alternator conversion with built in voltage regulator is mandantory NEGATIVE GROUND. Infact, ALL alternators require negative ground. (its the solid state gutts)
If you are going to use the OEM 6 volt frontmount coil, then you need a 12 to 6 volt converting resistor. Ask your parts person, they know. I don't know because there are several 12 to 6 volt converting resistors made by different parts companys and they all work.
After you get your 6 volt frontmount coil wired for 12 volts using BOTH the "infamous ballast resistor" AND the 12 to 6 volt converting resistor in series like flashlight batterys. You should read about 3.5 volts (2.5 min, 4.0 max) at the OEM 6 volt square frontmount terminal with the points closed and 12 volt battery voltage with the points open. TIP: put tractor in high gear and push/roll the tractor big rear tires to turn engine to close or open the points.
If you haven't started your 12 volt conversion yet, I strongly recommend getting a 12 volt conversion KIT, it has ALL the parts you'll need and FOLLOW the kit instructions religiously...........good luck, Dell