I'd be in favour of replacing the stern tube with the thickest steel tubing that you can find that will fit.
Boracay has a cutless rubber bearing in a steel strut, so I'd expect that any competent machinist could make something for you. I be in favour of something with lots of metal thickness welded on.
The bearing on Boracay is held in place with a set screw - it was probably a tight fit to start with.
Welding of thick metal is a bit of an art, so a professional welder may be worth the money
Don't forget to leave enough room for a decent size anode, with maybe a couple welded to the hull
Finish it off with a quality stern gland (some may need water supply through the stern tube) and, apart from the occasional check, you may be able to forget all about it.