Hey Tony,
I have '76 Cordoba with 400 big block 2 barrel. Yes I am sure I need one. When I put the continuity light to the pos. lead, it blinks, showing me the voltage limiter is working. When I ground the pos. lead, the gas gauge shows full. It has a good ground on the unit, as I cleaned it, and regrounded it. So it looks like I need the 4051147 sending unit. You have found out what I already know. There is not one to be had. Hey, I want to thank you for your time, If you can think of something I overlooked, troubleshooting this, I will be glad to listen.
Again, thank you,
Chuck