Hi Pat
I have just done this on my latest project, an old Johan built up I purchased. I used .030' x .030' Evergreen square rod (P/N 131) to form the edges of the front windscreen. These were cut and glued with liquid cement, then trimmed to size.
After allowing time to fully dry, the basic shape was drawn on masking tape held over the window frame. I then stuck the masking tape on a sheet of clear Evergreen Sheet (0.010") and cut out the desired shape, slightly larger than needed. With very careful testing, trimming, re-fitting and repeating the procedure, I managed to get a piece that fit, without the need for glue. Took me three pieces, but I got there . It even conforms to the curvature of the opening. Hope this helps.