Had my mechanic replace my fuel sending unit last night to fix my inoperable fuel gauge needle.
All that work and wouldn't you know it, that's not the complete problem.
It appears that the Ebay seller from whom I bought my new instrument cluster didn't put the needles back on right when they swapped out the tip face for the non-tip face on the far right. That explains why I only get a little over 3/4 reading when it's full.