I replaced the plastic windows on my 68 Trade Wind with glass. As far as I know, Inland is the only source of the curved glass at this time. It was expensive, but no more leaks.
Not a hard job, but some PO had used epoxy or something to install the plastic into the window frame. The aluminum extrusions are soft and can bend if you are not careful. The final solution to getting the frame apart was a heat gun, it softened the epoxy and allowed the frame pieces to come apart to free the glass. Take your time cleaning the window frame. You don't need a lot of gasket adhesive if you really get the frames clean. The best way I found to clean the old adhesive was to use a scotch-brite buff in my Dremel tool. HD or Lowes has them and it really does a great job cleaning the edges of the frame where the gasket goes.