dual batteries

I would either add a second battery or a single huge one for more capacity.
Depending on you track that you run at, if you have a successful day they may hot lap you.
The electric water pump is great to bring down the engine temp rapidly but you may not have enough time to get a good charge. I lost races years ago because of this scenario when I could not get the car started when in the lanes due to inadequate time to charge. Not the way you want to lose. You could also then more safely turn off the field to the alternator without so much worry about the voltage falling to low especially with a capacitive discharge ( msd etc) ignition
Which does not like low voltage.

Just my opinion.

Duane