Not an engine in the same class as a radial but the Sherman tank engine called the Chrysler multibank engine was also a marvel of engineering by taking 5 Chrysler flat head 6 cylinder engines then arranging them in a radial fashion around a single output shaft. Oiling was a nightmare as it had to be a dry sump. the 2 engine blocks mounted at a down angle had a tendency to trap oil in the cylinders behind the pistons. When the engine sat for periods of time the retained oil behind the pistons would seep around the rings into the combustion chamber. which could cause the engine to lock up the next time it was started. I only ever worked on 1 of those but I seem to remember an automatic compression release to vent not only the compression but allow any oil in the combustion side of the cylinders to drain away.
Jon is so good at locating these things maybe he can be persuaded to find a cut away of one of them.