IMHO the bowman design is clever, simple design and easy clean if needed. Heat transfer surfase of the tubestack for coolant is 11.2sq/ft, and 5.4sq/ft in the oil cooler tubestack. the oil cooler should be enough, it is equal to 20"x3" pressed oil cooler. cant find any heat tranfer surface specs for MRcool and seakamp fresh water coolers.

oil vs freshwater tubesatck










Oil cooler









Fresh water tubestack