Last shipment for this round came, now I have to order the push pins!
Antenna is not exact, my orig. 'Cuda had a one piece mast, it did not extend.
It all depends on the car's original radio. You ordered your original car with an AM/FM radio, so it was built with a solid 31" mast. Cars equipped with AM-only radios got a telescoping mast. It's as simple as that. My first Challenger was an AM/FM car and had a solid mast. My best friend's '74 'Cuda was built with an AM-only radio and had the extensible mast.
Since you've got an FM radio in the car, extend the telescoping antenna to about 31" tall for best FM reception. If you want to listen to talk radio out of, I dunno, Ohio, stretch that baby as high as she'll go... just don't forget to put it back down afterward!
The rest is technical and restoration nonsense.
Why the different antennae for different radios? It's a physics thing involving broadcast modulation. The ideal antenna for FM (Frequency Modulation) channels is 31" because the wave amplitude, or height, is constant, with the
distance between waves (frequency) being how the broadcast is modulated. At 100MHz, an FM wave is roughly 10' in amplitude or height. While a 10' antenna would mean optimal reception, it's not feasible for a car. But antennae work well in half-wave and
quarter-wave lengths, so a quarter-wave antenna is a perfect compromise. A quarter-wave FM antenna is ~31". Solid masts on other makes are the same length.
AM stands for Amplitude Modulation, which means the
amplitude (height) of the waves changes while the frequency remains constant. At 1MHz, an AM wave is nearly
1,000 feet high. As such, with AM signals the longer the antenna, the better--but a quarter-wave AM antenna would
still need to be almost 250' tall.
AM signals can travel much,
much further than FM ones. I used to listen to WLS out of Chicago--250+ miles distant--regularly in my parents' driveway as a kid. On a good night, it was as clear as any local station (with my 31" solid mast, no less). If you remember "border blaster" radio stations in the late '60s and early '70s, those were usually 100,000-watt AM stations broadcasting from Mexico that could be heard clearly 100+ miles into Canada.
On other websites, there's a long-standing debate about which antenna someone's car had originally. Guys who bought their cars when they were two years old and swear they're 100% stock say they're AM-only radio had the 31" FM mast new, and vise-versa. I certainly think some incorrect masts were installed at the factory, but the car was littered with build sheets and a fender tag so I doubt it was commonplace. One of my co-workers from decades ago was a dealer mechanic throughout the musclecar era, and I think his explanation solves the debate:
Per my old pal Orange, people used to leave the antenna extended driving into the garage, or an automatic car wash, whatever. The extensible antennas are fragile and would break. The techs got tired of replacing masts, and people got tired of paying for 'em. When dealership personnel noticed cars coming with a factory solid antenna mast, they found the part number and put a few in stock. A solid mast fits in any garage and is hard to damage unless you're trying. Nobody ever came back for another mast. He said he "probably did that a couple hundred times over the years." Happy customers were more important than factory correct. Lending credence to his explanation is that he worked at the local Chrysler dealership, so we're talking about new and very-recent, mostly original-owner cars still being regularly serviced by the dealer.
In other words, if you didn't buy the car new, you have no idea what was done to it before you took possession of it.
I think they stripped the hole for the voltage regulator, I don't remember nuts & bolts on the other car? 
So it's getting close to fluids time, got the 10w30 oil, pulled my left overs off the shelf, does this stuff go bad it's been up there over 10 years? 
REar end gear oil, I have 1/2 gal left over, but the guy who did my bearings recco'd using something a little thicker what should I buy? 
Also need to buy spark plugs, what should I buy, there's a ton of new things out there, any of them worth it, or just go with autolite or motor craft?
