the simplest way to do it is just with a single diode and a battery like a small SLA, problem is if the output on the stator is too high it will kill batteries because the battery is soaking up the power and turning it into heat as it eats itself alive.
slightly more complicated is t-ing in a simple 1-wire regulator with the diode and the battery. i just had a '75 DT250 that i wired up like this because it has a slightly oddball OEM wiring harness and i wanted to do some upgrades without rewiring the whole thing, t-ing in the voltage reg just kept my battery from cookin' you can still use conventional headlights and tail lights which are running off AC and only the battery and pump circuit are DC.
best option is definitely the floated ground, full wave regulator/rectifier, battery and full 12v system.