There is plenty of reading on this topic. Just google all of it up.
http://jeepdraw.com/John_Barton1_Shovels.html
http://jeepdraw.com/John_Barton2-AXES.html
These are addressing WWII axes in John Barton's review but the same specs still applied in the 50's.
The 53 & 56 ORD 7 SNL G-740 lists ax FSN 5110-00-222-0455. This
equates to:5110-00-222-0455, 10501970, 40D1FG, 6150925, GGG-A-926,
GGG-A-926TY1CL1DEA, MA207-21880, MA20721880, AX,SINGLE BIT
Kevin Emdee of Starr Electric posted this Pioneer tool write-up on the G503 several years ago:

This part of Federal Standard Part Catalog GGG-A-926a makes it quite clear what size ax head we use.