I remember them two speed clutch type set-ups. The problem as I recall is that they were weak. They had a 'sprag' [a 'one direction' device] in one of the jackshaft sprockets
View attachment 273840
View attachment 273841
. The attached is a two speed trans that I, years ago, decided would be the high-zoot trans for a mini. It has a handle on the side to shift between high and low and a neutral. Don't know what it came off of but as can be seen by the tag it is from ENGLAND [not the politically correct 'British Isles']. It has 'ALBION' on the side cover. Albion was the outfit that made all the 4 speed transmissions for early Triumph, BSA, Royal Enfield, Matchless, AJS limey bikes. Been on the shelf for years as I never did anything with it.