Help choosing the right converter/charger?

I wouldn't be afraid to put a c/5 charge rate into those batteries. That would be an 86A charge. They may not always be low enough to take that. I would say anything between 50 and 90 amps should be fine. When charging from a generator instead of the grid I think a bigger charger and thus shorter gen. run time is better. A 4 kW generator shouldn't have a problem running even a 100 amp charger.