That`s a slick setup. Built one years ago for charging my late brothers trolling battery on weekend fishing trips. Also works as an improvised AC source with a http://www.theinverterstore.com/?gclid=CJLxkMHplLoCFXRp7Aodwx8Atw sine wave inverter.
I can vouch for it`s effectiveness.
I put one together a while back with a 3.5 HP horizontal shaft engine with a coupling to the alternator. The coupling parts were from the same company. Makes a really nice set up. A friend has a horiz rig made on an old power washer base.
Far better than trying to charge batteries with a regular battery charger.