You asked about the OEM part number for the 1963 Galaxie fuel gauge sender. Here's what I got from my 1960 - 64 Ford Car Parts and Accessories Manual. I'll give you page numbers and section numbers too if you have access to the books. From the IPB, Page 298, Section 90, base part number is 9275. From the text manual, page 440, Section 90, the full part number is C2AZ-9275-D.
'60 - '64, big cars (except Station Wagon), Gauge Assy, Fuel Tank Unit. Gauge and outlet tube assy. Service package includes COAF-9276-A gasket. Gasket, fuel gauge, tank unit is made of buna rubber, 2.41" ID, 2.58" OD, 0.125" thick. A little part number fun to brighten up your day. Of my four "toys", the '66 F-100 and '64 Falcon have OEM fuel senders and are fairly accurate. My '63 Galaxie and '66 Mustang use AutoMeter senders and are not accurate (yet). Fortunately, both of the last two have accurate AutoMeter speedometers with trip odometers so I can use those to tell me when to go open my wallet and cry. Hope this is of some use to you.