tachometer retrofit for Yanmar YSM-12

[Kabloona]

My '79 Bayfield 29 came to me without the optional tachometer. I have run down the sender – available locally. But it seems that I must import the appropriate tach from Japan. The total for the two approaches $450. Even the two suppliers who have been researching this for me state that $400+ for a simple tach seems a lot! Apparently a basic tach that runs off the alternator can often be gotten for other diesel engines for under $100. Has anyone had any experience retrofitting a tach and sender on a one-cylinder Yanmar diesel?