Jack, I can tell you of my experience with the fuel gauge and sending unit in our 52 pilot house, I purchased a new sending unit from Robert's and installed it and it read full all the time the key was on. so I contacted Dan Ohora in Seneca Falls, n.y. phone number 315-712-0071, and told him how mine was working, so he asked me to send him the gauge and sending unit, and he would get to the bottom of the problem.
in a few days he called and said he found the problem, it seems in the 40's and 50's Chrysler engineers did alot if experminting with resistance,
they built some units that were 0-78 ohms resistance, some units that were 0-100 ohms resistance and some units that were 0-200 ohms resistance.
In my case the unit from Roberts was 0-78 ohms resistance, but my gauge was 0-200 ohms resistance, so the two would not pear up.
so the end of the story was that he built a 0-200 ohms sending unit to match my gauge, sent them back and I installed them and all works fine.
now you know that part, I hope maybe it's of some help to you, what I've found we won't live long enough to learn it all the hard way--good luck---Ken