Fireguy49, there's a couple good right ups on converting to 12 volt on here and I think Jim Carter trucks. I just followed them. I didn't mention heater or other motors sirens .... Because my truck was pretty bare of electronics. Don't forget to get that pulley for the alternator . Use an air impact wrench and leather gloved hand to remote pulley nut, comes right off, no struggles with wrenches. I' m real happy with results. Your truck looks pretty well loaded. You might want to keep it 6 volts. You can get 6 volt Pertronixs to replace points if that was desired.
Spanky, my tires are 9.00x20 .