You need a spacer for the plastic fan. Mini Mania sells them.
The later Spridgets with the cross flow radiator used a duel belt pulley and it was thicker to keep the fan away from the timing cover breather can.
If you are not running this timing cover, the plastic fan will work fine on the original single belt pulley.
It will not hit the radiator, it needs to be moved out from the engine by 1/4" if you have the timing cover breather and even then it will not hit the radiator assuming the car was never hit in the front.