On the -6, there was a detail that covered this in the canopy drawings.
The windscreen rests on top of the forward skin across the front, but there is a vertical slot cut in the skin along each side which creates a tab towards the aft end of the front top skin. The windscreen is slid down into the slot, and the tab covers the aft bottom edge of the windscreen on both sides.
I'm sure there is a better way to explain this, but if it isn't clear, look at the plans again and again and you'll find it.