Ditto on Kery's comment. The load imposed by a generator/alternator will be mostly determined by the load on the circuit. Generators develop a magnetic force that opposes their rotation. This force is directly proportional to the actual current flowing through the generator and going to the load. Low load = low force and low HP required: Higher load (more current) = more force and more HP required to turn it.
If the alternator is in any kind of shape, the load of the bearings and belts/gears will be nominal.
I would look for any inexpensive 12 V alternator that will supply enough current for your load (lights). Car, truck, golf cart, whatever. You will also need a small battery to supply the field current and to smooth out the output voltage. And a voltage regulator to control things.
Make it fit.
You can't win and there is a penalty for trying!