I agree about the baffling number of engine variants for a common type, like the xO-360s. Many of them are basically just slight revision changes (lighter crankshaft, different harmonic balancers, etc), and I guess the FAA considered those changes “significant” enough to warrant a new model? It can’t be that all of the variants are from airframe demands, can they?
Ugh, and the -D models. I don’t know how those ever got approved. My club went so far as to get a -337 to change out a -D model engine for the non-D model (it weighs slightly more, but is otherwise the exact same engine) in one of our aircraft.