Thanks to all, including Gary W, Bloo and all the others who chimed in; I never expected such a lengthy and informative discussion!
I had to drop the tank and remove the sender to do work (unlike the service manual states.) I then checked the resistance and found I had 32.2 ohms when "full", and .9 ohms when "empty." Since this appeared to be within tolerance, I was happy with the readings: I think that (as Bloo stated), there is very little I could do to get the upper number any closer (as you need to grind off the stop, thus actually increasing the resistance.)The lower number was certainly within range.
With the tank laying level on a table, I Used a straight edge to eyeball the distance between the bottom of the tank and the flange for the sender. It measured about 7 3/4" Then, I took a measurement from the bottom flange of the sender itself and the lowest point of the float, and found it to be about 5 1/2." I then bent the float arm down to about 7 1/2" and reinserted the sender into the tank,
then checked the resistance readings again (tank level, then upside down, as mentioned.)
After reinstalling the tank, I poured in between 5 and 5 1/2 gallons, which put the fuel gauge right on the 1/4 full mark; this should reflect the 17 Gal capacity; first mark at about 5-5 1/2 (4 Gal plus 1-1 1/2 Gals. reserve.)
BTW, I'm keeping my fingers crossed about the high end reading!
Hopefully, I have solved the problem. However, IMO, the vendors of these fuel senders should caution the prospective buyers that they will almost probably have to titrate (i,e., bend) the float arm to suit their particular application.
Thanks again to all,
Charlie Drake, Potomac, Md.,1940 Buick Super