Hey Jimmy. You are correct. The build date for my R100S is June 1978. It dies have the 1981 Brembo brake update and a Dyna 3 ignition as well. The brake upgrade moved the reservoir to the handlebar. I still have some things to do to get it into the shape I want but it is a hoot to ride.
see you at the Laurel Highlands next year.
86 K100RS EML
2007 F800ST & 2014 F800GS & 2014 F700GS