I repalced mine a few years back with new but cheap one I found at the WEST Marine surplus store in Oakland. I had to make a SS adaptor plate however. One thing I found was that going that way I had to do a lot of fiberglass build-up between the headliner and the deck so that the hatch would have something solid to mount on. Your solution looks like it may avoid that.
It's great to see Cal 29 info on the site... seems we don't get no respect in most sailing forums.