Dash speaker size??

[texjake]

What size speakers or speaker can replace or fit in the dash on a 68' with the original radio & A/C? I was able to find one post where some guys have custom fitted two 4" shallow speakers in the dash. I was wanting to know if a 5x7 or two 6 1/2" speakers can fit in there? The ones I have are not shallow, just regular aftermarket speakers. I plan on replacing the AM radio but I'm sure the new deck will be about the same size as the original radio, so at this time the speaker ohm's & the radio ohm's are not an issue, I'll make sure all that matches. I'm just concerned about the size & space under the dash for some better sounding speakers. Isn't the original size dash speaker a 4x10?