Robert,
I did a tutorial
HERE on how I replaced the windows in my Dino.
Also, I am pretty sure I replaced the front windscreen in my/our M1 Carte de France
HERE
If the shape is too complicated to make out of flat acetate and you want to try the heat forming (smash forming) route, there are a gazillion tutorials on the web if you Google vacuum forming (like
this), For simple shapes you don't really need the vacuum, you can pull the heat acetate over the original part (I did this for headlight covers on the Revell 612)
HTH