I thought my later one would not fit my early car because of the pin layout, but later realized the pin layout is deceiving.

and while it seems the 5 holes on the sender are evenly spaced, it seems the sender prefers a certain orientation over others to install.

I hooked up sender, right side up fuel guage read Empty, and upside down fuel guage read Full. I think the fuel guage in my 1975 is bad cause this is the sender from my 1975 and its fuel guage never worked.