Converting 28VDC -> 14VDC at around 200A How do you pull that off with that kind of current?
"28VDC" will charge two 12V batteries in series, but I doubt that will be of much help. 

If the generator is capable of 200A at 28V and if you only need 200A/14V, you can probably fiddle the regulator on the generator to get 200A at 14V (half power) out of it. That would be the cheapest solution if it's feasible.