1968 AMX Radio Speaker

Sorry for the confusion. Our AMC radios can work with speakers rated at 4 or 8 ohms. The monaural (non stereo) radios used only one speaker that in earlier cars was rated at 3.2 ohms which was an industry standard impedance rating at the time. Later, sometime in the mid to late 60s to early 70's, the speaker impedance rating systems were changed slightly so 3.2 ohm rated speakers became 4 ohm rated. Other speaker ratings at the time were typically 8 ohms and 16 ohms. These ratings were a hold over from the old days where radios and audio amplifiers, both automotive, as well as those for home use, used vacuum tubes. These early solid state (transistorized) AMC   radios, primarily made by Motorola, can be safely used with either 4 ohm or 8 ohm impedance speakers as long as you're using only one speaker. When used with the rear speaker option a fader control was included that compensated for the impedance of the two speakers working together.

Not to get too technical, but an impedance rating is not quite the same as a resistance rating even though the rating is still measured in ohms. Think of resistance as DC (direct current) rating and impedance as being an AC (alternating current) rating. A speaker works with an audio signal which is an alternating current. It also happens that a speaker is a form of motor. Since a speaker has moving parts and those parts work within a magnetic field the "resistance" of the speaker's voice coil varies with the audio signal as this coil is moving within a magnetic field. This motion increases the "resistance" of the speaker as it operates. This increase variation is on the order of 2X to 10X the actual DC resistance measurement which is the minimum rating.
The long and the short of it is that you're safe with any single modern speaker rated at 4 or 8 ohms. You want to keep the "load" the radio see's at about 4 ohms or higher. If you go much higher than 8 ohms then the radio will not be able to deliver as much audio power into the speaker as the power output goes down as the speaker impedance goes up. Conversely, as the speaker impedance goes down the radio's power output ability goes up. Having a speaker impedance load of less than about 3 ohms draws too much current from the radio and under certain conditions, like having the volume control turned up too loudly, will overload the amplifier's power transistor(s)and potentially cause a failure.

The speakers sold today, are with very few exceptions, far, far better than the OEM speakers that were used in our cars. In addition, these new speakers use much more efficient magnets, voice coils and other key parts so by using one of the new, modern speakers your radio will play more loudly and have a much better sound quality even with the limited output power capability (about 4 to 5 watts) of our original equipment radios.

Other than the visual cosmetics, which you can't see anyway when the speaker is installed, there's no reason to use the OE speaker or to have one reconed. These AMC OEM speakers were of the lowest sound quality. Simple paper cones, nothing special at all. Any of the new, modern speakers, especially those that offer a separate tweeter, will produce much better sound and in most cases are more efficient as well.