Can glass ttops fit in place of plastic style ones

yes, but they hafta be the right style pins, as GM had 3? different style glass ones, one of which was the same as the plastic

I want to say they used the same pins from 1985 or so all the way through 1992, so most glass ones should fit. I have glass ones on my 91, originally came with Lexans like yours though. Just make sure you swap the lock cylinders too so you don't have to carry around an extra key with you!

The actual pins themselves are the same (on all the "pin" style tops), the later years have a plastic sleeve that retract as the pin is forced into the mount - but the pins themselves are the same, so the end all answer is yes, the glass tops will fit just fine. I have 1987 glass 'Bird tops in my 1992 Camaro.