Excellent questions! I am doing the same for my 1966 Satellite. I have the tach and sending unit but I am not that far along to hooking it up yet. So this will be very valuable info for me!
Your tach sending unit looks in great shape. I am not sure mine will work. I am not so concerned with originality but more importantly is the functionality. Are there any sources for an external sending unit that will work if mine is no good?
Also, do you have to run all these new wires or can you splice into the factory wiring harness?
Did they really use 2 different wiring harnesses for tach or no tach? I know certain options were pre wired from the factory if you got it or not.
I have electronic ignition as well.
Hope someone (maybe with an original tach car) can help.