The rubber seal / gasket sits against the outside of the window opening so it shouldn't be causing the issue unless it is just plain stuck to the cab metal. You will need a new rubber seal so cutting it away would be OK. I suggest Steeles Rubber products for all your new rubber items - their quality / products are much better than some of the offshore stuff that others sell. What condition is your winshield frame in ? Mine was rusted badly at the corners and center " Tee " area. I ended up purchasing a new frame from Jim Carter's. If you are going to need to replace the frame, damaging the existing isn't an issue.
My restoration was a " frame off ", but I was fortunate the body was in pretty good condition / minimal rust.
Link to my pics is in my signature ( webshots )
