Hello RX7 Fans:
Thanks to your advice, I was able to get my bad factory power antenna out through the tail lamp hole. I ended up having to break off the antenna itself since it wouldn't retract all the way but then out it came without too much trouble. After you unscrew the trunk panel where the antenna is (just a few philips screws after you remove the little hole covers with a small screwdriver), the factory antenna is simply held on by two nuts inside the trunk, and the nut on the outside of the car body that tightens down over the antenna. Disconnect the power connecter to the antenna which, if you go to a manual antenna, you can just leave there after you're done. It won't hurt anything. The tail lamp, as suggested, is held on by eight 10mm size nuts on the inside of the trunk. The metal cover then wiggles out. It looks like it won't come out because the jack holding assembly is right behind it, on my left hand drive US model anyway. However, the copper colored metal cover slides out sideways toward the middle of the trunk..toward the trunk light, after you disconnect the wiring harness plug to the tail lamps. Hard to describe but you'll get it if you have to do this. Then the tail lamp pulls straight out the back of the car. Underneath that my tail lamp gaskets are pretty much deteriorated so I'm looking for some suitable gasket material I can replace that with later.
Installing the new manual antenna was pretty straightforward, with one problem it did take me a while to solve. The hole in the car that the factory power antenna goes through is just slightly bigger than the fittings that come with an aftermarket manual antenna. I solved this by getting two metal washers (make sure they're any type of metal that will conduct electricity as this is where your antenna makes a ground, and the better the ground the less static you'll have with AM radio). The outside diameter of the washers need to be big enough to cover the fender hole size, and the inner open diameter of the washers must be big enough for the antenna body to go through. One washer went over the top of the antenna base (the black plastic tube the antenna pushes down into), and down onto a metal "shelf" on the top of that. This is what conducts "ground" to the antenna. You may also need to install the metal "rocking horse" piece there that you took out with your old factory antenna. The one that came with my new kit was too small. Then the new antenna goes through the tail light hole up through the antenna hole with that metal washer and/or "rocking horse" piece pressing up to the car body inside the trunk. Holding that in place with one hand, put the rubber gasket half ball from the new antenna kit on the car body with the antenna through it (outside the car body), then put the second identical metal washer over that, then screw down the lock nut that came with the new antenna kit and you're done. You'll have to mess around a bit when you tighten the nut here to get the antenna oriented the way you want. I had to use a little silicone seal to attach the little plastic "chrome" finisher cover for the antenna base that came with the kit to keep that in place.
Important: When you have your original antenna out, be sure to take some sandpaper and reach up inside and sand the metal around the antenna hole from the inside. This will remove any corrosion there so when you press the antenna up against the car body from inside it will make a good ground. Then install the new antenna. And of course don't forget to re-connect the wiring to the tail light and connect the new antenna to the cable where the old antenna connection used to go. You'll see that right there in the trunk too.
It took me about three hours of messing about to figure this out so hopefully this will save someone a couple hours of aggravation I went through to make it work.
Steve in Arizona
1985 RX7 GSL-SE
Mind you, there's a lot less space int he FD for sound to move about in, and the armageddon exhaust probably doesn't help 