get a 6x9 mdf spacer ring. line up 6x9 spacer over 6.5 hole as best possible and screw into spacer using 6.5 screw holes or use self tapping screws or drill 1/8" holes and screw into those... screw 6x9 speaker into spacer. dont mind a few new screw holes but dont want to cut the parcel shelf.

im thinking of doing this only because my 6.5 pair died and my 6x9 pair works and i dont want to go through selling my 6x9 to buy another 6.5

seems doable though right?