Rather than quote myself from 4+ years ago, I will try to add some info to this.
The pics above are 77+ for sure.
The radios back then used 10 ohm speakers ( some 8)
That said; use this link, and READ the paragraph about Ohms just below the pictures on the front page.
http://turnswitch.com/speakers.htm
Fitment. A stock 6x9 in its Pass side location with a much needed "under cover" will surely be in contact with a spare tire that is 26 inches tall.
The mesh used in 70 on the package tray ( my '71 had it too) was Not ever substituted for a newer style cardboard unit. The mesh already had the speaker holes in them, which are visible through the rear window.
Turnswitch ( above link) does retrofit AM, AM/FM, and AM/FM stereo radios with newer tuner and amp and inputs for MP3/ USB and even blue tooth that are hidden. They also will run new technology higher watt speakers. So you could use that stock radio as a really nice modern radio and not even think about "switching it back in an afternoon" . More time to drive it!
PS. I have used "turnswitch" for a stock am/FM stereo radio upgrade and a dual front speaker. I have been Very impressed with the quality. The flip tuner still works too. Great product they put out, and newer 4 ohm speakers make this a win win.
PPSS.. 1 wire speakers used on am radio cars... UGH. Even with 2 condensors ( coil and fuse box) it was almost impossible to get rid of the engine ignition noise. If you Drove a car with this set up across rail road tracks in a city with street cars or electric rail system , you could kiss the radio signal goodbye for a while ( like and underpass, but more noise! .
addendum. The "fader" and rear speaker was a cheap popular add on( dealer install) for Am radios, very popular for cars going to drive -ins when they started transmitting the audio, vs a window speaker.