I WONDER about Spectra. Actually not sure if they're even fronting the 1966 Newport's unit. I certainly didn't find one in the 2 years I searched before settling on what I now have! Spectra makes EVERYTHING BUT a fuel sending unit for a 1966 Chrysler Newport.
I've seen a number of vendors for a unit like what I bought. I suspect the prior unit I had in my gas tank MAY have been a Spectra, of a sort not meant for '66 Newports. (I see in the 1966 catalog that the fuel sending unit, 14-72-1 looks like what I bought, not what I had prior, FWIW.)
IDK if the makers of this re-pop run out of Taiwan or off the mainland. I concur that there likely isn't more than ONE manufacturing source, thus my irritation with these people.
Just for laughs, I looked at the Spectra website and yes, they don't show a sender for a '66 Newport. BUT! I did find a listing for a '66 300, which I would assume would be the same as a Newport. I haven't double checked that in the Chrysler parts manual though, but I think it's a safe bet that the 300 (and other models) would share the same sender/gas tank/fuel gauge. FG143A is the part number.
Parts Results for This Vehicle
I've discovered that the listings for the old cars will sometimes need some creative interpretations. They will list something that they have good info that it fits and rather than take a chance on other models, they'll just omit the results. When you step back and think about it, it's probably wise.... Better to lose a little bit of low volume sales rather than annoy a couple customers that will do damage (through word of mouth, forums, etc.) to your reputation.
In fact, if you look at the listed applications for FG143A, you'll see that it's kind of a mish mash of what it fits. I'm sure it's low priority to refine the listings for Spectra and I understand it. Part of the hobby is dealing with this and passing the info on to others.
A couple things that I've observed though with other guys dealing with gas gauge problems and I'll bet your background can confirm this.
There is a lack of understanding how it works. The sender provides a resistance to ground and the gauge simply measures that resistance. No magic involved... With those absolute facts, you have the following areas where there could be failure of the gauge working and/or reading correctly.
First, and probably the most blamed (right or wrong) is the sender. It is an item that wears, no matter what happens. The wiper arm rubs against the coil and no matter what, it is going to wear. They weren't designed to last 50+ years.
Second is grounding to the sender. This seems to be very misunderstood. The factory added a small clip to provide ground to the sender via the fuel line. That was great when all was new, but again, 50+ years later, things like rust or the line being patched or replaced, I don't see as it's a reliable source of ground. A better ground would be to run a ground wire directly from the sender to the body. I've done this more than once with good, reliable results.
Third, and probably overlooked often, is the wiring from the sender to the gauge. It runs through a hole in the trunk floor, along the driver side floor and up into the dash. Another 50+ year old piece... If the insulation is broken, you have a direct path to ground with a resulting gas gauge that says "full". If the wire itself breaks down, either the gauge doesn't work at all or there may be added resistance in the wire that now makes the gauge read low. That simple fact is just not understood.
Fourth, you have to provide power to the gauge. Chrysler did a simple voltage "limiter" that works mechanically to provide 5 volts to the gauge. Another 50+ year old piece that is bound to fail. Good news is there are direct replacements that do this through the magic of half century old electronics and are very reliable and accurate.
Fifth, is the gauge itself. If you've ever taken one apart, this little gem of cheaply made junk will simply amaze you that most of them are still functioning. Chrysler had a purpose made tool that provided resistance to check these gauges. I have a eBay sourced, used decade box that works nicely to do this. Simply grounding the wire from the sending unit will show function, but not accuracy. Another misunderstood function.
I just read so many threads where understanding the function of the gauge is ignored and throwing parts at the problem is tried with utter failure and usually the sender gets the blame without even thinking about how everything needs to work together.
Edumacational rant off.