Hello,
I put a Kubota alternator on the B31, as the magdyno was sent to join the Prince of Darkness. I looked at commercial RR's, and the power dumping is horrible. I've only got 11 ponies to start with. My RR only conducts when the load requires it, and open circuits the alternator otherwise. The OC voltage is only 45v at 6k revs ( Rated speed, not the B31), and heat is not a thing. If you are up for a bit of electronics, I'll have a spare board somewhere. I did put load dumping on the board, but never bothered with it. The Kubota part is just a giant bike dynamo, but the 3phase requirement is catered for.