The shop manual confirms that there are only 4 'screws' (bolts), 2 on each side, that secure the frame to the body. They are visible with the top raised in ready-to-fold for storage position underneath the hinges.
I agree however that the job you're envisioning would be extremely difficult. I just received my copy of the Robbins top video covering how to remove and install a new top. There's quite a few detailed steps involved that are difficult to describe in words, but it isn't a job that I'd hesitate to do myself. If your canvas is so deteriorated that it wouldn't survive removal, it's probably not worth the effort anyway. And, if it's an original top, the windows are supposed to be glued in as well as stitched.
My top is in need of new plastic windows, but I can't find a source for just the plastic, and if I did, it would be hard to justify the work of removal, changing the windows (wife does have a leather industrial sewing machine BTW) and re-installation when you can buy a complete top for anywhere between $250.00 and $550.00.

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1986 560SL
2002 Toyota Camry
1993 Lexus