[Trevor Booth]

Iain,
well thats a start, you will at least know that the pump is to spec.
I would suggest that you try it before you start cutting up the plumbing system.
when you first get the car on the track you will have a lot of sorting in the first instance and that will give you the opportunity to check the cooling and collect some data.
If your cooling system is such that you need 50 psi I would cut it up!!.
Will the radiator take 50 psi. Are you running an oil to water heat exchanger, hate to burst that with too much pressure. Where are you going to get a 50psi radiator cap.
Too much flow can result in overheating as it is not in the radiator long enough and may create turbulence in the radiator itself.
The radiator manufacturer should be able to give you an estimate of the optimum flow rate for the BHP of the engine. He would be able to give an exact figure if he knew the heat rejection rate of the engine to the coolant. This should have been measured whilst the engine was on the dyno. He should also be able to give you the restriction through the radiator.
"This is what you need" is a very broad statement, how much of the aforementioned data did you supply them to enable them to say that you need 90gpm at 40-50 psi