Frank, I will respond, or tread where angles fear to, this usually stimulates others.
Simple answer try to keep it simple...
I am not familuar with your alternator and a quick check of their web site was not all that revealing (I did say quick).
So lets start at the bateries, from your description you will have a 4 x 100 A/h banks @ 48V a total of 800A/h. So maximum charge rate should be 10% so 80 amps.
I asume you have matched this alternator to the diesel, OK provided there is a charge regulator for the batteries, but this leaves a lot of amps to potentially go somewhere. Presumably via the inverters to the grid.
You say the alternator is essentially two, is it two 24V units or two 48V units? It seems to be 2X24v because of your mention of field voltage. Now any rectifier is best used at half it's amp rating. At 250 amps there is need for a massive heatsink. 250 amps X 1.2V(nominal drop across 2 diodes) = 300 watts not impossible but.
Ok so if it's 2 x 24 V they could be stacked so long as they don't share a common negative connection, this could be achieved using external regulators. I would expect each field winding to be isolated from each other and all other connections, so yes they could be commoned up.
So to your question, each phase of your rectifier will see an average 1/3 of the amps say 84A so IMHO your proposal is possible.
allan down under
