OldcarMark. This my understanding of date code deciphering from something Forum member Randy Holmes pointed me to from the Squarebird.org web site. An entry in a thread dealing with casting dating from an Alan Tast, author of the book 'Thunderbird 1955-66', references a Management Service Letter M-167a. The section I felt applies to the intake manifold you're looking at goes like this...
Casting codes begin with the use a number to indicate the year it was produced (Example: 7 is 1957)...
- the second figure may be either a number or letter to indicate the month as follows: 1 (representing January)-2-3-4-5-6-7-8-9-0-A-B (being December). [...that's because there are 12 months, but only 10 numbers]
- the third symbol is either a screw head for Cleveland built units (flat for the day shift or round for the night shift) or a letter for Dearborn produced units...
- next, to denote the day of the month that the casting was produced an A (1st day) through Z (the 25th day of the month because they don't use the letter 'I' ...
- then the use of an upside-down letter A (for the 26th day of the month), and the upside-down letters B-C-D-or-E for the subsequent days (27th, 28, 29, 30th) and finally an upside-down letter F to represent the 31st day of the month, depending upon how many days there are in the month.
IF anyone reading the above explanation has any corrections to offer about this, please share them. This is the only thing I've come across on deciphering casting dates. Frankly, I haven't owned or worked on any '50s FoMoCo vehicles where casting date correct components were a consideration.
Hope this helps!
NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York