Kevin,
Has the fan become more noisy compared to the past? Mine makes a real din when working , it is far louder than the exhausts on tickover.
I seem to remember that current thinking is to use a Spal fan, but I don't have a reference number for the correct one. Here is some information:
Click here Do not skimp on the wiring, the fan can pull 20 amps, and the standard wiring is not man enough for this , so upgrade and make sure you use a good quality relay.