The huge rad comes in handy, because you can reduce the airflow and consequently the noise. Heck one might even be able to run those two loops without any fan, if it's setup right!
I wouldn't expect much of a pressure drop from a radiator, given the 1 1/2 to 2" hose typically used, but it's going to depend on the flow rate. The flow rate is something that has to be decided, in order to select a pump.
In the mean time, you can run a manometer and see what kind of pressure drop that rad would give, at various flow rates (another bucket test?!?). It'll be very rough, but should easily put you in the ballpark, for pump selection.
Once you have the pressure drops of all the blocks and the rad, you can start looking at some pumps and see if they'll give you the kind of flow rate that you want.
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