Ah yes, it reminds me of the old days when I was a car audio guru.
As with most things in automotive electronics, not much is standardized. 6.5" is just a loose specification of cone size and not the fitment size. The size of the mounting flange of the basket, the depth of the speaker, and the size of the motor (magnet) are all factors that cause fitment issues. I do know that 6.5" with a deep mount and a large motor will not be a direct drop-in for the front doors. I have Alpine Type R 6.5" mid-bass drivers in the doors. I had to build a trim ring to give mount it far enough out so that it did not interfere with the window travel. Many an installer have, in error, mounted a large speaker in the doors just to have the customer run the window down and crack the glass against the speaker! Problem that I have is that with the volume about 3/4, the long throw of the mid-woofer hits the stock door grill. Crutchfield is a good resource for what fits.