Issa. I will post on this one as I would not want you to think you were being ignored.
No posts usually means, in the instance of a particular technical enquiry, that no one has any information to share.
What you are asking is a bit specialised, and you may be better off trying racing boat type forums, or even car or aircraft sites. The use of i/c engines in boats is now somewhat restricted to racing varieties, or old codgers who used them years ago. I suspect your engine may not be that old though.
Sorry Paul, you are not REALLY an old codger.
Ashley
##### this post contains adult humour considering the use of the word "codger" and should not be taken seriously, but with a pinch of (old) salt #####