Hey...Those are just vents that let the air flow outside the cab when you run your heater or air conditioning. Have you considered putting your 6.5's in the doors? They will fit perfectly with just some minor cutting to make the openings slightly bigger. I know this cuz I installed 6.5 components in my doors of my 1990 Mighty max. The holes are at the bottom front of the doors. Your 6.5's will sound better in the doors than anywhere behind the seat.

where do u cut to put the speakers in the door?