If this is a fairly uncommon minibike, I'm not sure I want to do any more "Customizing" or modification, than absolutely necessary, to get it on the road again. SO), if it doesn't have a provision for a jackshaft, then, it isn't going to get one. I used to retore old VW's (I worked for both US-based VW magazines before i moved to the redwoods of Northern CA) and I know that cutting, hacking, welding (other than remedial) and modifying a rare VW is very frowned upon by the Vintage VW guys..
(Maybe that's why they didn't like my 1957 VW sunroof, that ran high 13's in the 1/4 mile...:smile::wink: