I don't know anything about 850's, was there ever a front radiator mod done that used a front scoop like that? Although as you say, oil cooler seems more likely for the size of it.Was the scopunder the front bumper oor oil coolers?
My guess a radiator. Abarth used to mount thin radiators at that location on the 600.
Leaving the original radiator is place would certainly simply the pumbing and filling the cooling system. Interesting I don't see a water pump mounted fan in Franks car. Seems there wouldn't be enough room for a fan up front. The alemano doesn't have a fan, but then its a race car and doesn't need to sit idling at traffic signals. It has a 127 water pump, which is ok as the 903 is a reverse rotation motor.The other photo shows a radiator alonside the engine. Two radiators?