I'd say you have the resister wire to coil and full voltage to the Pertronix correct. Don't think it's your pertronix.
Backfiring makes me think timing.
Like spark plug wires maybe.
Firing order on those is one, two, three.
Distributer turns counter clockwise.
Did you have distributer out of tractor?
Normally there's a # 1 mark on dist cap.