I understand, although being able to see out the back at all will be a huge improvement.
Since the vinyl window that came with the new top on my weekender Boxster two years ago is already showing signs of becoming cloudy and scuffed, even though it's always garaged and rarely used, I've decided to go this route in the daily driver.
I actually found an upholstery shop nearby that specializes in Porsche convertible tops. They've done this conversion many times apparently and have their own source for the conversion glass window tops with a lifetime warranty on the glass.
The whole job was quoted at $1,400.
I don't think I can do much better so I made an appointment.

I'll let you know how it turns out.