The water pump cavitation brings up the traditional Pantera question of what is it? Is it a street car or a race car?
This is compounded by the fact that the stock 351cj has much more potential then the version Ford decided fit the character and intended use of the Pantera best.
As such, the engine is basically a 5,500rpm operating range unit. That's likely the high end operating rpm of the average new buyer.
Everything in that package is aimed at that. If you want to go higher, you start to show the limits of the package and need to alter some of the initial "settings".
The original engine has a by-pass in the water pump. That's how it is designed to operate.
Want to re-invent the wheel? Go ahead but why change things for the sake of change?