It's a bracket that was made by OMC and specifically for their engines. The engines that went on the Sea Drive has a slightly different mount.
My understanding is that internally the engines were the same but used a different mount.
If it works many people are dealing with it until it dies as the sea drive parts are hard to come by.
Very likely that the Sea Drive was used and a repower occured in 2000 or a rebuild?
Here is a good side view picture of a sea drive.
http://continuouswave.com/whaler/ref...tor542x640.jpg