So my 77 Ghia only came with the tiny dash speaker, there was no visible speaker set up on the doors, so i took a chance and took the door apart and saw that the hole is there, and the panel has the cut out , you just have to cut out the fabric.
Yep! If memory serves, a 5-1/4 will fit easily and will be a much better sounding alternative to the dash speaker! If you wanted to install speakers in the back, someone made a speaker that would fit the window deck, but I can't remember the size right now. I ended up just purchasing some 6x9s and using boxes. No one's in the back seat 99% of the time anyway!