A sawzall or jig saw would make short business of the extension. I think the challenge might be to put back the wood along the top of the gunnel that you screw the cap into.
Restoring it back to original would not be any harder than any other once you have the sheer line back and the hull gutted. Make sure you create a support structure to support the hull from twist and deformation. Then after grinding her clean, lay a few layers of epoxy and cloth on the insides and that will stiffen her up and make the rest easy. A clean slate. So it all depends on how handy you are and how much effort you want to put into her.
We have a ton of examples of FB rebuilds here to give you some ideas.
If you do want to sell her I'm sure another commercial guy will make you an offer. Down here, there are plenty of other Aquasports out there to choose from.