The last thing on my checklist before I attempted to start the car was installing a SPAL fan. I chose the 16" medium profile puller fan. It fit nicely on the radiator with plenty of room to clear the water pump.
Here's a shot of my mount idea. I wanted to keep it easy to remove in case I needed to work on something at the track.
The primary support is the lower 1/8" aluminum. This strip easily supports the weight of the fan and fits in the tabs for the stock fan shroud. Then the brackets on top hook over the radiator but are there as more of a backup in case something happens and the lower mount were to fail. Two screws into the upper radiator lip keeps it in contact with the radiator core.
To wire it, I cut the connector off the stock aux fan (my fan was all busted up so I didn't feel too bad) with a few inches of the stock 3-wires. The SPAL fan only has one speed so I twisted the high and low speed wires together on the factory connector and crimped them to the power wire on the SPAL wiring. Then just connected the ground wires together. This way the fan can be unplugged and easily removed.
One of the discrepancies in the engine harnesses makes it so that the normal aux fan speed will not work with the M52 engine harness. This is because on the M52 cars the double temp switch goes to the relays and then to the DME. On the M44 cars the double temp switch goes to the DME before heading to the normal speed relay. Without updating the chassis-side wiring the normal fan speed will not come on automatically in a M/S52 swap.
However, on both M44 and M52 configurations the double temp switch goes directly to the high speed relay. Stock M52 double temp switch is 91/99C and the M44 switch is 81/88C. So by using the M44 double temp switch and not touching the chassis-side wiring my SPAL will turn on at 88C, lower than the factory M52 setting.
Since doing this I have run the car and let it idle long enough to kick the fan on. By only wiring up the SPAL through the stock AUX connector and using the M44 double temp switch my fan kicks on and lowers the radiator temperature just as the stock fan would. The only difference is that my SPAL only has one speed. So it comes on at the "high" temp of 88C on the exit side of the radiator.