Hi,
I have a similar setup running a sevcon gen4 controller and a Motenergy PMAC in parallel with a 12hp combustion engine. Regen is tricky and I still have issues with regulating voltage and current. You should know that if you go for Sevcon there is almost no information to be found on how to program them and the CAN interface used for programming is $900.
The setup I'm running now uses 36V and during regen I get about 15Amp's, this could be a lot higher but I don’t have the skills to program the controller.
I'm working on a second drive train and I'll go for the Kelly this time. I'm also going for 48V but I only need aprox. 80 Amps of nominal power.
Im using the LiFeYPO4 Winston batteries in my fiat, luigi500.blogspot.com, together with the akumon from ev-power. And I'm getting four more for the boat. The akumon board can be used as a safety switch durin regen. If the voltage of each battery exceeds 17V the akumon will trigger a 12V signal that can trigger a relay that in turn disables regen.
Please keep us updated on your findings.
Best regards
Rikard