Glass Removal
Get a " Carpet Knife " with extra blades in the handle and use that to cut the old rock hard grommet away bit by bit until you can clearly see the edges of the glass all the way 'round , then and ONLY then , use the side of your fist to " bump " it here & there until it's fully loose .
99 % of the time , you'll get 1/2 way through this and decide to try and tip it out , the remaining bit of rock hard rubber is *very* tenacious and it WILL crack that old glass .
I suggest you do this first as you're almost guaranteed to find some rust in the pinchweld and if it's rust through , you want the cab firmly bolted in place when you're repairing that .
I hope you know to NOT buy new glass grommets from the host here , to go Steele Rubber Co. , they'll have an AMERICAN MADE , properly fitting one that won't leak and will last long unlike the Chinese crap .