Before worrying about fasteners and screws..
You should check the height of the 6x9 speaker frame.
Often this can be higher than the pressed metal recess which can cause the package tray to be raised and not to sit down properly. Also if the speaker is a multi-driver such as a 2-way or 3-way again check the height of the mid/tweeter frame you do not want the package tray to rest directly on this or one can get vibrations..

In extreme cases we have mounted 6x9s from below the metal frame. Key point is you want the package tray to have some clearance between it and the speaker, or there will be vibrations and rattles..
Or even restricted speaker output.

Just my $0.02..