I did a retrofit without much directions and I did not (don't now)
know much about building.
A problem I had: The fiberglass around the window has to have
some finite thickness. That means that the window will be recessed
or you have to have a way to carve a flange on the plexiglass. I
had no way to do that so my window is recessed. This is not very
good aerodynamically. Maybe I can fix that someday.
You need to use a thick piece of plexiglass and find a way to carve
some of it away along the edges to make the surface flush with
the underside of the wing. There may be a tool somewhere to do that.
I still don't know.
Bruce Hughes