It's odd your sending unit doesn't work from 521 restorations because both of mine are from there and mine still work great after 5 years so far and I noticed they are made in America so its odd yours failed. Could it also be why your truck isn't running properly? I've seen sending units cause stumbling due to sucking in air.
rebuilt the carb on the slant 6 it still bothers me that after all work making sure it s all good and clean and it still doesn't run perfect. thought my issue may have been between the gasket and intake so RTV'd it to the intake which may have helped but still had an issue. damn throttle shaft is sucking are also. tempted to glue a cap over it since it seems to be leaking the worst. hit it with brake clean and the engine runs a lot better. it does at least seem to be holding fuel so it starts a lot better after sitting where before it would leak all its fuel onto the intake when you let it sit.
i would guess it is not it is the original carb. it has a rebuilt tag so it was likely swapped at some point and with how clean the vehicle is underneath i would guess it has less than 100k miles on it. i will definitely have to do something with it. it really is not running consistently. .Man, that carb has some miles under its belt. I have never seen a choke shaft bore worn that much.