Friends have commented the hatch appears to be a lesser quality component compared to the overall favorable structural build of the boat.
Paul, sounds like you've done your research. Your boat, your choice(s)

Somehow feel that the analysis of this quote may be so far off the mark due to the lack of supporting evidence (NPI) & the issues that will arise from the choice to go with clear, flat hatches without non-skid, and moon-burn for early wakeups are yours, not structural at all. It's simply covering up a hole in the boat, with little support, regardless of the material.
Doesn't matter, 'cuz you've found what YOU want for YOUR boat.
Our job is to answer your question and help you find the best sealant or (not, oh, please, no) adhesive!

I do not recall anyone doing this, reportedly, before as you have described. Most have gone directly to "concepts" who advertise in
Mainsheet magazine
Your installation issues are cutting and sealing. The material and the size of your hatch, as compared to the existing opening and the curved shape, are critical. Don't know what your capabilities are with tools.
Sealant of the new cuts are important, and look to the options you may have to cover the new edges. Our MkI has a nice art deco vinyl cover screwed in.
I frankly do not know how to deal with the curve compared to the new what I assume to be straight edge of your new hatch.
Once you're done, the potentially slippery top side will be a cause for another solution that has appeared here or in the wiki.
More detailed questions, or progress reports would be great. Keep us posted, sounds like a really good new idea.