Front stereo speaks are 3.5" diameter. Probably need to find some with the OEM-type small magnets due to limited room issues. Most replacementrs will handle 100 watts of power, which is not needed, and also means a much larger magnet, too.
Rear speaks should be 6x9s, possibly with FOUR such mounting holes in the rear deck. Most of the coax or tri-ax 6x9s have a bridge to mount the mid-range and tweeters on, which increases build height and/or requires you use their supplied speaker grilles, rather than mount the speakers from the underside of the rear shelf panel under the factory-supplied rear deck board (with slots for the speaker's souind to come through). ALSO important to have some sort of grille cloth over the upward-facing speakers to keep accumulated debris from getting into them, too!
The factory "center front" speaker is also part of the factory stereo/multiplex 5-speaker equipment! Usually, it is 4x10 on the Fuselage platforms. So . . . 2x3.5 round speakerss for the upper corners of the instrument panel + 1-4x10 for the "center" or "center, off-set to the right side" for the total of 3 front speakers. With 2-6x9s for the rear speakers, run by a ganged front/rear fader on the instrument panel (mono rear speakers have a similar knob, but only one fader attached to it). For an ultimte total of 5 speakers in the factory stereo/multiplex radio sound system, on non-convertibles.
Enjoy!
CBODY67
Seems like there is a vendor on here that refurbishes factory speakers? Use the "Search" function to find that thread.