20" transom options on a 20' boat

[JohnB]

I am appealing to the brain trust on here to get some ideas.
Here is the problem.
20' early 70's potter SF w/ 20" transom that consist of air and crumbled wood.
I have a 20" 330 pound motor that I want to hang off from it. Motor is perfect, and paid for.
Options....
1. Rebuild transom just as it is.
2. Rebuild transom for 25" motor, get extension kit for motor.
3. Rebuild/close in transom, and put a bracket on it.
4. Rebuild trans to 25", and put a jack plate on it.

Boat will be used for inshore/near-shore, and once in a while, up to 20 miles offshore.

What are the pros and cons, and are their any other options I have missed?