@James007
I have not seen that version of the windshield bottom rubber thingie before - Maybe @Alan Merklin has - I suspect that it is for an original Speedster? This is a cross-section of the bottom rubber that I got from Carey at Beck, and the one on the right has been modified to better fit the metal rail riveted to the cowl of the car.
Do a search on here. Someone (last year?) did a few posts about about modifying the bottom rubber to actually get it to fit the windshield AND fit over the aluminum strip riveted to the cowl (for now, let's just call that the 'rail', OK?). I also posted on this in thse past in a effort to figure out just why they don't all seem to fit together - You could search for that, too.
Theoretically speaking, the rubber thingie is supposed to slip over the rail, but it can be a real bear to get it on there and get it to stay in place once the glass is inserted because all of the angles are wrong. Then, you have to get the glass in it and get everything joyously in sync. Believe me, I've tried it many times on different windshields and failed.
After I concede defeat, I do an Al Merklin trick and position the windshield into the rubber thingie where it's supposed to go (make sure it is even on both ends and DO NOT tug or pull on the rubber to get it to stretch because it's memory will always pull it back over time). Then, I just push the rubber thingie up against the rail from behind and then attach the top frame and Bob's your Uncle, you're done.