[elhigh]

Finding traction or implement drive motors in the 12v DC range will be hard, and for them to be useful they will be enormous.

I've been fond of the original Etek (now long out of production) and its many copycats, most of which are actually pretty good. Etek clones are useful at voltages from 24v up to 72, a nice broad range that you should be able to hit regardless of what generator setup you use.

One Etek clone to power your drivetrain and another to power your implements should get the job done handily. NOTE: a single Etek can generate well over 15hp, completely soaking up every bit of your gas engine's output. Obviously you will want to include some power limiting hardware.