Bondo is right (per usual) time to find a new used outdrive/boat.
I have been told many times that the motor would also have to be replaced with the outdrive, due to bolt patterns and input/output shafts. I haven't looked into it yet. However I know
Advance Adapters has been making t-case and transmission adaptor plates for a long time. I bet they could make an adapter for boats ... but it might take a petition or pre order list to get them to do it.
I don't recall the input/output shaft makers. Those often come with kits (i.e.
Slip
Yoke
Eliminator kit for 4wd), but I think I had come across a vendor when I was looking for info on swapping 4wd XJ parts into a 2wd XJ. If I can find it, I will post it here for you.
But when that time comes for me, that's what I will be looking into. As well as searching for an existing adapters.
When it's all said and done, this may be a more expensive route, and still does not address your mechanic situation. I live to far away to help you with that.
I would love to see some pictures, and more information about your boat. I have a 1965 Silverline that I am having trouble identifying my mc(?) parts.
Post a new thread for it (please), not trying to hijack this one.