[spareparts]

if you can get your hands on a Mercruiser installation manual it will give you the perfect measurements, they are not that hard to find, they usually put a copy of the installation manual with the engine opertors manual with each new engine. most people never evne know whats its for or ewven open it up, if you can find a Mecruiser tech, he probaly has one laying around( not to be confused with the service manual) worse comes to worse, i think you can find it available on line