Nice find.

Did you look up the actual date code or are you going by the model number.
Snap-on Date Code Chart
I used the information from the following website:
http://collectingsnapon.com/Site/Home-1.html
Quote
3/8” drive 1953 – 1978
The 3/8 drive was not as developed an offering as the ½ drive set at the end of World War Two, but through the 50s and into the 70s it seems (to me) that the 3/8 inch drive developed faster and into the dominate offering. There was a handle style change around 1953 that differentiates the older and newer sets. A sparkplug ratchet – the flex head – appeared and has become very popular. The plastic handled ratchet also appeared in large numbers. Wobble extensions also become available for the first time
I don’t have information for every year so the date ranges are the “known” ranges. It is totally possible, in fact probable, that the date ranges are wider than stated.
Snap on Model number Description Date range
E-10 Hex Lobular 1978
F-5L Ferret Sliding Bar 1953 – 1978
F-670 Flex head ratchet 1960
F-671 Flex head ratchet 1962
F-671 Flex head ratchet 1962
F-67-B Ferret Ratchet Adaptor 1953-1978
F-70M Older style handle Ferret Ratchet 1952
F-70R Older style handle Ferret Ratchet 1960
F-710A Ferret Ratchet 1952