lorne,
I have cut down 2 windshields on my bikes, I cut the bottom, that way you leave the nice clean edge on the top.
I tried a jig saw first but it created a lot of vibration, wound up using a spin saw with a fine toothed blade, it did melt the cut line some but I used an electric sander to smoth the edge.
Good luck.
I understand the concept, but how do you cover the existing holes when you drop the windshield down? Or am I missing something?