Is your keel encapsulated or can you see the bolts?
We have a different boat but had to replace our mast step over our encapsulated keel. The old one was wood and had rotted. We built a form in the place of the old step, poured epoxy (glass reinforced) and laid a plate of G10 on top then restepped the mast.
If your current set up has lasted 33 years it might be easier to have a direct replacement fabricated and come back in 2029!
Best of luck,