This is a 1939 case. It was cast in F(6th letter of the alphabet or JUNE) and the 8(we can assume was the year 1938 since the case is a 1939). This simple date code is used on all types of older H-D castings like engine cases, transmission cases, gear covers, etc. Sometime in the month of June, Year of 1938, hot molten aluminum went from a semi-liquid to a solid, cooled - and formed this case.
When restoring an original-type motorcycle, these date codes are important. Now we have motorcycles being built with correct dates codes, matching frames, engine cases, etc . . . being sold as "original motorcycles" where as the sum of the parts - were never together as a unit on the Harley-Davidson assembly line. The larger "raised numbers" denote the actual casting number(part number) of the individual part itself.