If it is ALL 6 volt then no resistor is needed. If it is 12v then look at the coil to determine if it is INTERNALLY resistor coil or not. If it is INTERNAL resisted 12v coil then no ballast resistor is needed. If a regular 12v coil (not internally resisted) then a ballast resistor is a good idea between coil and ingnition switch. If no ballast resistor is used on 12v then points life will be short.
IF weak spark then TEMPRORarily bypass (eleminate) ballast resistor and try that to see if spark improves. If spark inproves then coil mite be internally resisted AND or bad ballast resistor.
THose of u running a one wire alternator mite want to put something like a 40 AMP fuse on the wire that comes out of the alternator. If the one-wire alt suddenly kicks out a heavy dose of amperage then the wire or other wires could fry if they are not heavy enuf to handle the amperage. This could happen under situations of a very low charged battery or somekind of a short should a wire somewhere in the electrical system get pinched by brush or other conditions.