Bob,

I have a maramu with a Perkins M60 and have also looked at repowering as I have recently bought a new engine for another boat.

I installed a 75 hp yanmar in my non-amel boat and for various reasons kept the old gear box. The engine and box both had SAE4 bell housings so I thought it would be straight forward. However the shaft out the PRM260D box was too long and the damper plate I got didn't match up. After the expense of fabricating a spacer and machining the damper plate all is good but the moral of the story is next time I will get the engine with a gear box already attached. I don't think you can get a yanmar of the shelf with a ZF25 (new version of HBW250) but you can get a ZF30 with 2.7 ratio off the shelf. The ZF30 is similar but rated to a higher HP than the ZF25.

Unless your old gearbox is free of corrosion and is quite new I would recommend renew and try to sell the old one with the old engine. If you get a Cummins or other you should be able to get a suitable vertical offset gearbox such as a ZF25 ZF25H or ZF30.

John