Personally I would go with your thought of making yourself a vacformer to create your windscreen, you carve the rest of the car so you might as well make a buck for the screen to vacform. If you are going to try and bend the screen you have already cut out for the Maserati you could try the hot water method to easily and instantly put a permanent curve into the plastic.
To make the headlamp covers on a 1/24th scale Revell Ferrari 250GTO I used a round implement (a handle) of the correct circumference,
Wrapped the plastic sheet round the handle and held the ends in pliers. Put some water from a boiled kettle in a dish and held the plastic in it for a few seconds.
Removed it from the dish and held it under the cold tap for a few seconds to cool it.
Stuck the masking tape templates onto the shaped plastic and cut them out.
The plastic covers on the Ferrari - the larger of the two cars in this picture.