Hi Blue,
Perhaps some help from the South-West of The Netherlands. My clubmagazine "The Unapproachable" (Norton Club Netherlands) recently supplied some details about K2F magnetos.
AC is for several twins of 1948-1957, such as Ariel KH, BSA A7/A10, Matchless Super Clubman, Norton 7 (= my bike), 77, 88, 99.
RO is for Triumph 5T, 6T, T100 & T110 of 1955-1957.
And if ye really want to know, contact Theodole in The Netherlands (theodole-king-of-darkness@planet.nl), a well know Lucas specialist in The Netherlands.
Have you got a serial number, e.g. 42111A, beside the AC or RO mark? It'll give more detail about the bikes the K2F is meant for.
Gr. RIVO