I've got a '75, and I put my 6-disc CD changer in the glove box behind the passenger seat. I ran the controller cable through the center console to the radio/Cd controller (Custom Autosound USA-5). Once I got the 'right' cable, it worked like a charm. The original cable that came with the radio/CD changer plugged straight into the back of the radio, and had an 'L' plug for the changer. The straight controller cable plugin on the back of the radio kept getting hot from the engine/firewall, then crimping and messing up (it's a tight fit behind that instrument bezel, as I'm sure you already know). Custom Autosound sent me a cable with 2 'L' connectors -- one at the back of the radio, and one for the CD changer -- and I haven't had any problems since. By the way, I had to remove the cardboard glovebox insert to make the changer fit. I fabricated my own 'false bottom' for the g/b, but don't keep the jack/lug wrench there anymore, anyway. If you want more specifics, just let me know.
I did the same fabrication as ala75vette. I put the custom autosound 6 disc cd changer in the jack box. I mounted mine on end so i could change the cd's while driving pretty easy. I also fabricated a new storage tray to fit in there and hold my octane booster and t-top tie downs. send me an email and will send you pics and installation help if you still want it.
Sounds like Wamp and I did basically the same thing. I also mounted mine "vertically" with the provided brackets on the rear-most wall of the compartment. Like Wamp said, when in the car it's fairly easy to access & get to the CD magazine. I also drilled a hole in the "lip" in the front/top of the compartment so I could pass the controller cable under the carpet down to the center console area, where I then routed it to the radio. I'll echo Wamp's offer of assistance if you'd like to email me, also.