the 12V coil WITH the resistor, with a 6V battery, will NOT put out a good enough spark when cranking to fire well .... the resistor on a 12V system is bypassed when the starter is engaged, allowed back in the circuit when the engine is running .... if you ditch the resistor, it MIGHT work, but if you're going to do 6V, do it, quit jumpin around in circles, make a plan and stick to it
not sure I understand spending money on 12V stuff, then turnin around and buyin 6V stuff .... you're going to need a lot of parts anyway [probably including most of the light bulbs], why not stick w/ 12V and just do it?
and NAPA should have charged the battery for you if it needed it, how do they know it's good if it needs a charge off the shelf??
Bill