It's a 3 speed, 2 port with 5.5bhp. It should have a 15mm carb as standard. This was the first of the large frame motors which eventually led to the PX. You can fit a 4 speed gearbox straight into the cases and change the selector parts but it would still be VERY slow. It's probably not worth a lot 'cos unless you're doing an origional spec restoration to a VBA then you can fit any later motor from a sportique, super, sprint or PX into your frame.
I might try to advertise it on the classic scooter forums, for all those old gits who don't like you to change anything.
What happend to your Harley, Pup? It all went quiet.