I remember some time ago someone on here said that they sell new fuel
sending units with an adapter ready to install on our early 66 Chargers.
I have the sending units in stock - on my web site at www.uscartool.com
66-67 Charger fuel sending unit had a 5/16 connector. Suggest using a 3/8.
The 66-67 Charger 3/8 fuel sending unit was for the Hemi; it would be a nice upgrade if you have modifed you engine to make more HP.