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How to size a cooling system??

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I am working through my conversion project, and the motors and batteries are going in. Now comes part 2, bringing it all together functionally.

The battery-packs have water-cooling, the 2 motors have water-cooling and so do the 2 controllers. So, I need to figure out water cooling. Thing is, how much/how big is big enough?

The original ICE-version of the car was not super-efficient at maybe 10 mpg in 1959. Say I allow for 30 years of technological advancements in engine tech, and the same car with a 1990's engine would have been maybe 12-15 mpg.

At 75 mph for an hour, that means say 5.5 gallons of premium. What I found on Google says that 1 gallon roughly equals 8 kW, so that's how I get to 45 kW per hour of driving. If anyone has a better estimate, please leave a comment. Freeway driving is not city driving and all that, got that, but for the sake of figuring out the cooling it's probably not a bad number to go with??

Question #1 is whether all of the 45kW effectively translates into heat, or is there some portion that goes somewhere else?
Question #2 is how much a normal radiator "exhausts" per square foot (??) at 100 kmh/60 mph at say 30 degrees outside?

If a few people with working cars could reply with what they've seen for
- weight of their car
- running amps for freeway commute speeds
- cooling set-up
- driving conditions (uphill&down, stop&go) and operating temperatures
then I can try to find the common denominator and see where that puts me...

Thanks in advance for helping out, RK