choke wiring again

Hopefully your coil doesn't get 12 V if the ignition switch is off or your battery will run down. Hopefully you also have an Ignitor II or III, since I understand that the original Ignitor requires that you keep the ballast.

The "unused" terminal on the back of your alternator needs to be used, i.e. connected to a good ground. The factory did that by leaving out the ceramic insulator and bolting the spade to the frame, a sometimes iffy connection to corroded aluminum. If you have a later "square-back" alternator, with 2 isolated terminals, you need to run a jumper from one to gnd. Ditto if you have 2 isolated terminals on a round-back alternator (not the way they ship). With your 1968 alt wiring, the other terminal gets a variable voltage (0 to 12 V) that is adjusted by the regulator to control the field current and thus the output current. If still the old mechanical Vreg, it is actually switched on & off. Regardless, it isn't a steady source of 12 V ignition power.