If you were able to get or find the engine you are looking for you may not be able to run it.
Due to insurance cost and law suits most areas to run boats have ban them.
Rick

Heres is a place to try but I doubt whether you are going to get a match. I have a Rolls Royce Merlin Engine I made many years ago, but its a bugger to start and run. Swore I would never build another Engine that wasn't steam.
Some things are almost impossible to miniaturise.
Good Luck

Agreed as an ex Model Engineer, this is looking at something that few people will do.
I believe that China are making some!

Are you seriously saying you want a miniature Chris Craft B - four-cylinder petrol engine.😝
I know there are a few very cleaver engineers out there but I don't think they do these as a business, but more a hobby.
But good look with that 😁