I have a coupe that was modified years ago to a roadster before I got it. It still needs restoration so it's pretty rough. But they never put a top on it. They just did a very poor fitting of plywood around the back. You'll need to figure out a way to finish the cut edges but it's doable. The...
If you're using plain water adding anti freeze will also raise the temperature the water will boil at. If you're just barely hitting 212 at sea level it could make the difference.