There have been a number of companies who've made or make radial engines. The afore mentioned Technopower
makes 5, 7 and 9 cylinder engines and has quite a history. Saito makes a 3 cylinder, OS makes a 5 cylinder and Seidel in Germany probably made the prettiest. There are others but these come to mind. I've owned radials from most of these guys at one time or another.

The greatest challenge will be keeping the engine cool enough yet hot enough to run well. It you run glow you will need an elaborate glow driver, if you run ignition and glow fuel be prepared for much higher temperatures. Gasoline and ignition is out of the question if the engine is aircooled. You'll only be able to do it if watercooled. you don't have the luxury of the airflow
you need. I have experience with four cycle engines in tanks and boats, at present I habe a 1/10 Sankyo type 74 powered by a O.S. 48 Surpass. I run it on glow ignition but still after 40-45 min of running it needs a rest, I use a belt drivn fan. I originally ran it on gas ( tiny NGK ME -8 plugs) and it started and ran wonderfully; I use a throttle couple timing advance to minimize backfiring and ease of starting. But I'd only get 10 min of run time on a cool day before the engine got so hot the fuel boiled out of the carb and the engine stopped. As it is I use a stainless steel header and exhaust system which has a limited life span.
4 cycles run hot(er) than two cycles. For those engines that use chromed aluminum cylinders( Saito) overheating isn't an option. This a greater part of the reason I didn't carry out my plan to power my King Tiger with a Saito 90TS. I also had plans
to build a 1/8 Tiger I and power it with an O.S. Flat four( Pegasus) 320. I had the engine, ignition system, starter and gearbox
but decided the logistics weren't worth it. Cooling is the name of the game. Even when I ran large gas boats( Kawasaki, Tanaka(Tas) and Kioritz engines) during the 80s (as well as tanks) I learned cooling the engines that were buried in a closed hull required good airflow AND water cooling.

I also have two 1/8 Sankyo type 61( at 113 pounds each- you see one in my avatar) that are powered be aircooled Zenoah 23ccm gasoline engines. They get monstrously hot. the method Sankyo employed to reduce heat buildup was to minimize the restriction ( read no muffler)
in the exhaust system and make it VERY short. Makes for a largely unpleasant model to run for long periods....

The idea sounds great and no doubt could be made to work but even I won't spend the time to do it until viable water cooled
multi cylinder engines are available. I have no interest to build an engine like that either; not for a tank anyway...

Jerry