U79 Rear Speaker Mounting

[69-er]

Can anyone describe or point me in the right direction as to how the rear speakers were mounted?  The passenger side with the hey holes match a a typical modern 6X9 pattern but the driver's side holes don't match.

Is this what is used to mount the passenger side?
 

[Danzo]

This is what a factory install looks like. Phillips head screws through the grille. Single power wire connection. The "metal tab" is to ground the speaker.
Doc