Garth's illustrated fan blade article is great! For the bargain hunters among us, if you decide the small OD Cortina 8-blade fans can be had a few bucks cheaper from E-Bay instead of a Pantera vendor, some of whom stock the assembly shown, be aware they were originally used as a sucker fan mounted directly on 4 cylinder Ford Cortina vee-belt driven water pumps. They have an oversized center hole that's filled with DeTomaso's steel adapter parts #69 and #71, plus the four metric bolts shown in the Gr-3 catalogue. This kit adapts the fan to a Lucas DC motor shaft, mounted backwards to become a ring-shrouded pusher.
Without those adapter parts, the bare plastic fan(s) will not fit anything except a Cortina water pump & pulley. Of course, if you own a lathe, some scrap metal and have a Saturday free..... People who bought the 8-blade kits from a vendor decades ago say they do in fact help lower water temps a little with stock fan motors. But today, more powerful pancake DC motors and matching larger dia fan blades move 4-6X more air than any fan blades run by stock Lucas DC motors.
When I wrote my fan/DC motor article a decade or so ago, I used an E-Bay anemometer to check actual air flows for a whole number of fans, but I never bothered to check the small Cortina 8-blade. I had a pair of 10" DC 4-blade sucker fans in a full shroud on our Pantera for a couple of years. In a test on Judy's favorite highway on the way to 'Vegas at 150 mph for ten (10.0) minutes, water temp slowly climbed from 200F to 230F on a calibrated 260F gauge. I slowed to 90 mph, & water temp slowly returned to 200F. Later that year I changed to 14" shrouded Flexilite 10-blade sucker fans; a repeat test at the same speed & road the next year showed no high-speed temp creep. Dunno about 180 mph; my tires, like my body, are getting on a bit....