Think someone mentioned years ago that the windshield on the Envemo (not sure if applies to both cab and coupe?) was not Porsche stock size - and difficult to come by.
I watched episode of the original Top Gear where they had a US model winsheld with the correct curve cut down to correct size. Now, that's even more stress that just fitting a Speedster whindshield. The Fiberfab Aztec7 kit car uses a Lamborghini Miura windshield - price that one out! as it may cost more than the car its-self. Many kit cars use various year Corvette glass often turning it up side down or using the rear glass for the front windshield.