Here’s a pair of Mark 58A’s on a Feathercraft Clipper. It was a lot of work setting this up but so fun to run them. My understanding is that you don’t get double the horsepower of a single engine due to drag and such. Much more efficient to run one single larger hp engine, but the “harmonic hum” of those two engines running together is a real treat.
https://www.youtube.com/watch?v=wQxqO6TNksI&ab_channel=M00seontheloose