There is one other advantage to electric fans.
That is that they can be attached directly to the cowl and can have tighter tolerances.
You may be able to fine tune your arrangement, though often they are quite good oem.
Lessening the gap improves airflow.
If all else fails, it is one more approach available.
An auxiliary fan can be added just to the trans cooler if needed too.
If you use a pusher fan, be sure it's one that's reversible.
If the noise doesn't bother you, you could put vents in the hood or just pop the hood open.
Be careful of aerodynamics though.
Airflow around the hood is often counterintuitive.
I have naca ducts in my hood which appear to be intakes, but since they aren't sealed, act as vents when stopped.
With any movement. the area become pressurized and they cease to exhaust.
They may actually be reducing radiator airflow somewhat.
Due to the streamlined nose, I have to run a fan at most lower speeds to get enough cooling, as air lifts and flows over the grille.
Ducting air behind the radiator for maximum engine cooling may be a good approach.
Normally front ducting would be important, but beyond making sure there is no interaction between the front and back air, I doubt it makes as much difference at 5 mph as it normally would.
There are a lot of flex fans.
Most are quite shallow.
The deeper ones have a blade perpendicular at rest at the tips.
Use the deepest possible blades with 6 or 7 blades.
The oem quality fans have double reinforcement and very deep pitch and are usa made.
$150 most places for a full size and $80 was the best price I found a few years ago.
There is a big difference in quality on those and since the consequences are so severe with failure, not a place to scrimp.
But the fixed blades flow more and are cheaper.
Just get the most aggressive ones.
The last one I got was about 5 inches deep.
I don't think you'll have any trouble with cooling.
How much weight do you anticipate?
If you don't get a new radiator with larger tanks, you can add capacity by adding a tank to the system.
Besides adding capacity, it can be cooling by radiance from the tank.
It's best to add it to the intake part of the engine, inline from the radiator.
This will give you extra cool fluid, especially useful on startup from a stop.
There may be aluminum finned pans for the oil.
I'm sure there are for the trans and rear.
Canton can make larger capacity oil pans, if you think you need that.
An accusump adds capacity without causing overcooling issues and prelubes the engine on startup.
Taking too long to warm up oil, or worse, not ever getting warm enough, is almost as bad as overheating.
Here's a spal electric fan.
http://www.speedwaymotors.com/Spal-Curv ... ,1783.html
No brand listed but this is a high flow fan.
http://www.speedwaymotors.com/Heavy-Dut ... ,1846.html
The better flexfans should have a brace on the blade that goes full length on the blade.
There are normally staggered rivets too.
This one looks the same except for those missing parts of the design.
http://www.speedwaymotors.com/Chrome-an ... x-Fan-15,3