Here's my experience with my '63. I don't know if it will be the same, but they do share a lot of parts once you get past the skin.
- My '63 had what I believe to be a factory-installed rear speaker. It doesn't have a lot of markings, but it looks just like some pictures I've found of NOS Mopar rear speaker kits from the period. The trim tag also confirms it should have been installed. (Thanks, Torky!)
- It was definitely 6x9
- The speaker mounted to the underside of the rear shelf, from the trunk, with simple sheet screws
- If you line up carefully, there are already holes you can use for the screws, no drilling!
- There is an identical 6x9 hole on the passenger side - cars with a rear defroster use this as an air intake for the blower. If you look up a Mopar rear defroster from this time, you'll see it is also, obviously a 6x9 shape
- My rear shelf panel disintegrated when I removed it, but it had perforations on both sides to match the holes in the body
- Are you using the factory radio, or something modern? This will have a lot of impact on sound clarity and speaker choices
- The speaker was 4 Ohms when tested with a multimeter. Some people claim old speakers are higher resistance, but both the electrical diagrams in the FSM, and markings on some NOS rear speakers I've found support the 4 Ohm rating
- The factory radio only expects 4 ohms on that rear circuit, so if you want to run two speakers with the factory radio, you need either run two 8 Ohm speakers in parallel, or two 2 Ohm speakers in series. (
How to Wire Speakers in Parallel & Series, and how does it affect Impedance?) However, there's not really a point to this complication, since the sound will still be mono. You might as well just run one speaker in the stock location
- Keep in mind, the factory radio is anemic by modern standards. Maybe 10W per speaker? So you don't need massive 100W RMS speakers.
- With factory radio, the radio is your limit on sound quality. It's designed for mono, AM radio, so even the best speakers with a clear hole cut in the shelf won't make much difference
- If you're installing an aftermarket radio, all bets are off. You can do whatever you want.
- Depending on your speakers, you may need to use a small spacer/gasket (which may come with the speakers) to keep the cone from bottoming out on the body, which will sound bad
Here's a picture of a '61 or '62 (not mine) with a speaker and rear defroster installed.