I really prefer to have a puller fan but the clearance between the water pump shaft and the radiator precludes any single fan. I could have tried to fit up a pair of smaller fans, but I didn't like the CFM ratings of what would work with the room I had. I tried to find a reference for CFM requirements vs HP produced, good luck there. I did find several that gave a CFM recommendation based on cylinder count, useless. Pretty sure a 300 HP 4 banger is going to need more airflow than my 97 hp flathead 6, but that's not how the cylinder count recommendation works out.

After some research and thinking I ended up with a Derale 18217 fan. Designed to work as a pusher or a puller, 1800 cfm on low speed, 2400 on high speed. I did some airflow measurements with the stock fan that I will post up later once I have the numbers for the electric fan.

Some might wonder why I wanted to go with an electric fan. Well Engine Masters did a Dyno Shootout and the type of fan I have took 30+ HP to spin that style of fan at 5000 rpm. My stock flathead put out 97 HP when it was new. That's a big chunk though the EM fan had 6 blades, mine has 4, they ran a shroud, no shroud on my setup and If I ever hit 5000 rpm on my flathead I won't be worried about fan HP loss but rather why my rod put a hole in my block, lol.

Here's a shot of the stock fan setup, my Trusty Assistant is pulling the radiator.