Size of speakers that fit rear panel

What is the size of speakers that can fit rear metal frame panel of Mustang 1966? 6x9 or 5x7 ?
Coulnd't find the info anywhere on the net.

Best Regards
Marcin

Those that you saw mounted in my car are JBL GTO528. They fit without cutting, but are round in an oval hole

But you might be able to fit in bigger ones if they are oval

- Kim

If you want to hide them under the cover, make sure you buy a flat model

Thank you so much for help Kim !!!
(y) (y)