On my Oday 23, the mount is attached with machine bolts that are readily accessable through the big cockpit locker. When I replaced the outboard bracket, I also replaced the bolts. I also had to repair the big block of fiberglass that is between the bracket and the transom. Water had gotten inside and rotted away the wood core. I scraped out the rotten wood and put unthickened epoxy inside to firm up what was left. I added a few sheets of new glass cloth wetted out with epoxy on top. I redrilled the holes and was good to go.
I picked my replacement bracket so that the existing holes on the block and through the transom could be reused. The Garelick two stroke mount sold now should accommodate the original Oday hole pattern. However, if you are thinking of updating your outboard to a four stroke, you may need to do more work. The four stroke motor mounts have a broader base and will not likely fit onto the existing block (which will be too narrow). This means you would have to make an adapter for the existing block (maybe a stainless or fiberglass plate), or make a new block. I've seen them made from plywood or Starboard.
Is it necessary to have a motor mount that is specifically rated for four strokes, or can a robust two stroke mount deal with a four stroke engine? You will find many threads on this and other sites discussing the issue. Some say that so long as the mount is rated to handle the weight of the engine, it doesn't matter if its a two stroke or four stroke; others have said that a four stroke creates so much more torque that the two stroke mounts can't handle it. I'm not an engineer and don't play one on TV, so I will keep my opinion to myself. Do your research and make your own determination.
