It's been my suspicion that the aluminum pump housing was more to save weight than make things work better. Which can be important in the racing orientations/uses.
Almost all water pump designs are pretty similar in design orientation. The actual components might be done differently, but the basic functions remain the same. It all depends upon a good, stable flow of coolant into the pump and heat exchanger items for things to work well. At the rpm levels a typical C-body would turn (with 2.76/3.23 gearing and taller tires), cavitatioin should NOT be an issue, I suspect. 25mph/1000rpm with 3.23, 28.66mph/1000 with 2.76, typically. Torque curve peak in the 75-90mph range. Cavitation at those rpm levels would point to something majorly wrong in the cooling system.
One point is that the factory engineers and accountants compromised on designs that would work well for the vast majority of customers. For those that needed something else, there were the factory trailer-tow packages or police package items. Sometimes, in trying to second-guess their actions, we make more problems in the process . . . sometimes not for specific niche applications. In some cases, having a correctly-optioned vehicle is more important than in others. Just getting "factory air" resulted in many equipment upgrades from the "base vehicle". Bigger radiators, fan clutches, fan shrouds, water pump, HD front torsion bars, etc. NOT the same as "adding to" a base vehicle and hoping for the same good results, in the aftermarket.
As things have evolved since the time our cars were designed, there have been some items which are now OEM that can be good upgrades. The aluminum or composite radiators (usually with greater fin counts) is one. Long-life coolants might be good, if you're starting with a completely "new" system (rebuilt/hot tanked motor, new radiator, new heater core, and new hoses). Maintaining the correct freeze protection is necessary, no matter what.
I found a BASF handout back in the 1980s. It spelled out that you changed antifreeze as the additive package wore out. The additive package had the task of keeping the ethylene glycol from eating the solder in the radiator and heater core. When the additive package was depleted, then the attack on the solder began. So change it before that happens. Modern systems have gaskets rather than lead-based solder.
Enjoy!
CBODY67