Serious search. I can't offer much but I'll toss a couple pennies worth of thought.. I last saw a drive like that in Jersey 20 years ago. One was hanging on a 24 superboat. As I recall it was called a sternpower. It too was being called a speedmaster. In my search at that time I found Eaton had some parts available for it. Much of it was NLA. My guess is the drives have been replaced. Most often Bravos are the go to conversion. I suggest widening your search away from those drives.

Good luck