I am assuming 18W per headlight, which means (if my math is right) about a 1.5 amp draw per unit which should work just fine. The biggest problem is going to be pulsing without a voltage regulator (or rectifier). The incandescent bulb is not affected by the pulsing but gets dimmer the slower the engine turns. It still gets the pulsing signal just does not go from dim to bring as fast as a LED so its not visible to the eye.
In short, yes you can run these but I would add a voltage regulator.
--Daniel