I purchased a gasket on spec when I was doing the gradual collection of parts for the restoration of my 142. After getting the gasket, on closer examination of the body around the missing windshield I discovered that my car used the later bonded glass. The gasket is still sitting in a box of parts in my garage untouched. I got the gasket from Iroll motors. Try Iroll to see if they still have them or send me a private message if you are interested in buying mine (I am obviously never going to use it). I might have the original invoice (I was tracking the total project cost because I like to poke myself in the eye on occasion) with the part number on it.

On my bonded windshield car, the dash went back in after the new glass was installed. So you should be able to R&R the dash with the glass in place. On my bonded windshield, there is a plastic trim piece at the bottom of the inside of the glass which hides the area between the lower edge of the glass and the top of the dash. This internal windshield trim piece just clips in; but, needs to come off before you lift the dash out, otherwise is will get broken. The gasket style glass may or may not have a similar trim piece. Other wise, dash removal is pretty straightforward; but, tedious.