All automatic C3, C4, C6 FMX as well as Ford Top loader 3 speed, 4 speed and peanut 3 speed manual transmission bellhousings are casted with a Ford factory casting number, followed by a date code.
To find the date code, you need to remove the bellhousing from the transmission. The date code is located on the back side of the bellhousing. Look for a small circle with a number in it. For example 64, 65, 66 and so on. A series of very small bumps appears around the number in a circle. Each bump numerically represents one month of the year. A 68 with 4 bumps is decoded April 1968. 11 bumps would be November 1968.
Decoding Tip: Most cast aluminum engine and transmission parts, as well as brackets, are decoded in this same manner.