Before I removed the upper panel, I decided where I wanted the defroster outlet and drilled a 1" hole as per plans. Removed the panel. After deburring, I marked the 4 rivet locations on the defroster flange and drilled pilot holes. Note the screen segment sandwiched between the flange and the panel.
Updrilled the holes to #30 and riveted.
Note: time for this opoeration is included in the other post with today's date; I split over two posts so I could post more picture.