I have a Sterling with a rotary turbo. (I didn't build it.) The radiator is up front. It presumably gets decent air flow but the radiator is of modest size. It has dual electric fans that seem substantial. What I can say it that the fans run a whole lot AND the car still gets a bit hot when I'm in start-and-stop traffic.
You can put a radiator almost anywhere as long as it's big enough and a decent amount of relatively cool air goes reliably through it. My dad has built more than three dozen homebuilt aircraft and I've often been fascinated in the subtleties of airflow over those engines. All have been air-cooled. The difference between having one of those engines run hot vs normal has often boiled down to adding or subtracting a simple baffle to direct the air or adding a little lip on the exit to tumble the air (resulting in a low pressure area for the air to exit into.) That experience has always made me think more critically about airflow through my cars.
A radiator can be placed in the rear of a car -- if you can find the space -- but you have to find a way to channel air to and through and away from it. Flow of fluids can fool you. I immediately think of several different episodes of MythBusters that show how air above the bed of a pickup truck simply tumbles over itself in an eddy. Some of that bubble of air never really leaves the bed of the truck. Areas like that aren't necessarily obvious.
The rear scoops on the Sterling are pretty much just there for looks. The upper "cup-holder" scoop was meant to be a relatively static source of cooler air for the carbs. The lower scoops are essentially there to look cool. They don't "cool the brakes" on a car that has drum brakes and is only driven to car shows. And the lower scoops empty into...nothing. Mine immediately spill over the end of my rear torsion bars and go nowhere coherent. In order to get a radiator to function in the front or rear, we have to find a way to direct a modest amount of air directly to the face of the radiator -- with no alternate routes it can spill around. Then we need a low-pressure escape for that air (which actually is the easy part at the rear of a car because there ARE low-pressure pockets at the rear of the car.) As a bonus, the air should be fairly cool to start. In Letterman7's "Rose" car, both of us are pretty sure that the air would exit that big radiator that was embedded in very rear surface of the car BUT there was never any clean cool air TO it. The air in that car kind of spilled in through the engine compartment, over the (very hot) exhaust and at best kind of tumbled slowly through that radiator.
I didn't find the video you're referencing but I think I remember having seen it. I get really worried about any radiators that are essentially over the Bug transaxle because of how hard it is to get cool air to that location. Air will NOT come up from under the car -- that air is already a swirling sheet that pretty much stays between the ground and the bottom of the car. Even if you rework the lower side-scoops and add baffles to direct air, you'd need to turn several corners to put the air into the front of that radiator, and each time a fluid turns a corner it impedes the flow considerably. I can almost see it working if a person had a substantial roof scoop that harvested air from the top and redirected it down and through a radiator BUT then like you said, there is no visibility out the rear. Cameras help -- and every Sterling should probably have one -- but there's no substitute for good old site-lines.
I spent a lot of time with one of my cars trying to decide whether to use a dual radiator setup in the rear in which each radiator was essentially behind a wheel well. I had myself convinced that I could open up the upper side-scoops to make them bring in ram air, directed with baffles over the rear wheel, delivered to those locations. But I couldn't really make the radiators (mock-ups) fit in any sensible way. Plus that put even more weight behind the rear axle with is something I was specifically trying to avoid. Also I had read a bunch of stories suggesting that the flow of water through a dual system can really fool you and you might only have one side that's really working due to path of least resistance, etc.
Due to all of the above, I could never, in the end, justify any radiator location other than up front in the current configuration of our cars. Even then, it's hard to find a way to lean the radiator to make it fit under the hood. You have to either tip it pretty far rearward or almost flat forward. And the builder still has to strategically direct airflow so that air gets directly to the face of the radiator with no escape routes, and then allow the air to exit to an area that is relatively low pressure like top surface of the hood or fenders or maybe into the wheel well. (I've never been able to convince myself as to what the environment of the wheel well is actually like.)
My personal opinion for radiator position in a Sterling roughly distills down to this:
Most favorable:
--In the nose/front trunk, big as possible, w/ carefully considered airflow management
Possible:
-- Dual radiators behind the wheel wells (maybe -- I couldn't quite make this work geometrically)
-- Single radiator in the very rear (maybe, but it's ugly and you need to feed it cool, ram air)
Least favorable:
-- Dual radiators in front of the rear wheels (I couldn't find enough space)
-- Dual radiators up front (there is NO advantage to a single one up front and lots of disadvantages)
-- Radiator(s) above the transaxle or on top of the engine deck.
I always try to state my biases and limitations to my advice; I have never tried a radiator in the position of the one in that video. If it works, fantastic. My guess is that it exists within a tumbling bubble of hot air and therefore is likely NOT gonna be efficient. I like how Rick described it as that he'd never take his eyes off the temp gauge. I'm like that in my "good" red car (rotary turbo). When I'm in traffic, my eyes are absolutely glued to that gauge (which is silly because I wouldn't even be able to do anything if it did totally overheat except just pull over.)
I think there would be different options if the car was a little longer between the firewall and the rear axles. If there were more space in that area, perhaps strategic scoop and a radiator could work. But those aren't the dimensions of our cars.
