Ever mount speaker in defrost hole??

I'll measure it when I get home. But it sure looks close to 6x9 . This is on a 68 F/B, (there is no pkg tray in a F/B) but I've seen the same blower setups in the package trays of a-b-c bodied cars and they are mounted on the pass. side of the pkg tray (in what looks like a speaker hole) with the vent coming up thru the middle of the pkg tray.

I guess I could make an adaper of sorts, but it would be pretty slick if it fits the way it is !