the class pre 84 means the year the motor was made, & has nothing to do with with the frame. mutley.
Where did you get that idea from?
You can have a frame thats been built later but it must be a replica of a frame of the era, eg pre85
Evo = no disc, no watercooling, no linkage suspension
Pre 85 = bikes built up to & including 84 models (85 models built in late 84 aren't eligable)
Depending on what god you barrack for Evo bikes built in early 80's can ride in Pre85 but not vice-versa