Mike, I had a '77... It had a regular 12vdc water pump, not air pressure charging. I'd highly recommend a regular fresh water pump.
As for my two cents about your possible purchase: -it all depends on whether the coach has been used several times in the past couple years, or if it's been sitting. If it's been sitting, you could be in for a costly fix/replace ride. Things like brakes, cooling system, furnace, etcetera tend to go bad if not used ("use it or lose it").
Also, the 440 was a strong engine, but had tendencies to crack the cast exhaust manifolds. Finding the right replacement could be a real problem (they don't make 'em anymore, and for my '77 there were four different configurations for the exhaust manifolds, but only one would fit the coach because of the brake m/c and starter locations). Some people went with headers, but they put an awful lot of heat into the engine compartment, so then you need expensive high temp plug wires & shields.
Overall, if the coach has been used recently and runs well, it'll probably perform well for you too.