If the dash has already been cut, that should relieve all the anxiety and will really open up your options. I have the 67/68 dash, so its a bit different, but I do have the kick panel speakers and they look really nice and are positioned so the sound is decent. Since you have a coupe, I would use the package tray for mounting a set of 6x9's instead of using the rear quarters, since there would be no permanent damage that way.
Good luck!
Kelton