Sure, 6x9 will fit in the rear on all of them. '69 'verts used a cardboard dish that screws to the trunk floor/seatback area. The repro cardboard pieces are too shallow for high performance speakers as they were made for the vintage speakers.

I put the subwoofer in the trunk and the 5 x 7s in the well covers, and have unobstructed sound with the top down and the boot on. You can't do that with the factory mount points.