I just became a partner in a 1977 32' Marinette equipped with 318's and velvet drives. I have 2 Mercruiser 325hp/ 350's sitting at my shoppe. I am looking to repower using these motors mounted to the existing velvet drive transmissions. I can handle everything in this conversion, but I have no knowledge of what will be required to mount the velvet drives to the GM based Mercruisers. Is there an adapter plate available to convert from the Chrysler 318 bolt pattern to the GM block? Or do I have to Purchase new bellhousings??? Does Anyone have the part numbers required for said conversion???
Any help or guidance on this subject would be greatly appreciated.

I am not in big favor of junk yard parts. What would really be appreciated is adapter parts numbers. I guess I can just call borg warner and ask for numbers. The real issue is the drive numbers have all but desintigrated and was hoping someone could give me correct numbers for the drive.

Thank you for your advice. I Googled m&m in New England and did not see them, but there are plenty of these bellhousings on Ebay. Could you provide a model number or some type of model designation for me to order a rebuild kit for the port velvet drive??? This transmission is dragging in forward even after proper shift adjustment and fluid changes. We will be installing mercruiser 350's. The Mercruisers I have in stock right now are both standard rotation, one of them needs to go to the machine shop because it sat with water in a cylinder for two years, this motor has only fifteen hours on it since rebuilt. I know this motor has got to go to the machine shop for repair. My debate is if I should get this motor setup for counter rotation, or should I leave both motors standard rotation and set the rebuilt transmission to supply the counter rotation for the boat???
My other concern is that the boat has 1" prop shafts with 1 to 1 ratio velvet drives. Can these 1" shafts with 1 to 1 drive ratio handle 350 hp at 4800 rpm. If so what is their max hp rating at 5500 rpm. I know it sounds nuts to ask for these targets at these rpms for a 32' (with flybridge removed), but I am an engine builder, The motors will be built to sip gas between 3,000 and 4,000 rpm but this build will result in 400+ hp between 5,000 and 5,500 rpm.

One of our (insane!) members has a 32 footer converted to 454 big blocks running 1:1 drives and 1 inch shafts. And it's still afloat (from what I hear). I wouldn't be concerned with 'only' 350s.

All small block Mopar bell housings for the later design (ie: after the old polyshperical motor) are interchangable, so if it's for one of these 318/ 360s it will work.

Jeff

Sounds like it would be the least amount of trouble to just rebuild the 318's. You would not want two engins turning the same directions. So if you go with the 350 you will have to change one to counter rotating.That means a new crankshaft,cam,dist,water pump and more. I would at least take the Cryslers apart and see what they need.