The format of that number indicates that it was an internal number used during production to identify the part as a component of an assembly to differentiate it from other similar parts being built into assemblies (they wouldn't want a Ranchero/Station Wagon frame rail on a sedan frame) and they usually use such stampings as a cross reference to the source of the material used in the part, or it can also indicate a specific vendor that Ford contracted to build sub-assemblies from which they built the complete unit. If you look around some more you're likely to discover the date code of when the part was actually built (and the format of those stampings in your pictures suggests they are not date codes). Most major sheet metal, castings, and steel parts include a date code indicating when the part was manufactured. On my Rancheros the date codes are stamped in about 4 places on the frame rails two up front on either side and 2 in the back near the wheel arch. Date codes are located in various areas, and are normally comprised of 3 or 4 digits. TYPICAL DATE CODE: 2A21 2 = Year (1942/1952/1962/1972) A = January 21 = 21st Day of the month Since your car is a 1972, the frame could have been built between September 1971 through September 1972, so 2A21 is decoded as being built on January 21, 1972. MONTH DATE CODES: A - January B - February C - March D - April E - May F - June G - July H - August I - (not used) J - September K - October L - November M - December I might have guessed that it was a date code except for the format which would be October 14th February 5th so that doesn't exactly work out for your items.