I have a '69 convertible and it has factory 4 x 6 in the kick panels. I also installed Blaupunkt Overdrive 5 x 7s in the convertible well covers; these were the only speakers that would fit the space and allow the power top to operate.

I've seen 5 1/2 in the doors, but just watch your rear clearance with the glass down. I don't think you can get them in the kicks without serious cutting.