Close as you will come to getting an OEM fuel sender..

Some of what you found could be quality control related. We never know if a previous buyer has handled an item then returned it to the seller.
The traveling contact, be it brass or copper, is the softer metal. It will wear away before wearing through the resistor wire. Its size puts 2 or more laps of wire under it in any position. Higher pressure = faster wear. It needs only to lightly touch to complete the circuit.
I certainly wouldn't be happy with it as received/shown in your 2nd pic. I dont know if I would attempt to fine tune its mechanical form, or return it for exchange.
One of your measurements is 0 degrees equals 36.4 ohms. I know that resistance should be close to 1/4 tank. So if 0 degrees is presumed 1/2 tank, where is the fault? Picture suggests your fixture holds the sender at plumb. It is not plumb when mounted in the tank wall. Even the vehicles stance has a bearing on that walls angle. Consider the shape of the tank and it gets quite complicated. "did a little unscientific testing" is all any of us do.
You can calibrate your gauge to that OEM limiter power supply. The multitude of owner using alternative power supply such as the 7805 solid state regulator would see slightly lower needle positions from same resistance values.
At the root of it all... we are dealing with 40+ year old technology, very basic thermal range indicators for gauges. We don't know how much exactness the factories engineers put into these senders. Those owners who put too much trust in the things back in the day would learn their lesson once stopped on the shoulder, out of gas.
I probably will try one of these senders next time I need one. Meanwhile I just be glad that gas prices are down, pumps are on every corner (that wasn't so back in the day) , and keep plenty in it.