As davidwa has previously mentioned The Ryedale Rally in North Yorkshire accepts ANY street legal machine.
We have previously had old BSA`s, a Sunbeam, Royal Enfields, old BMW`s, Honda 90`s, we have even had some Peugeot scooters.
All the above machines run in the trailbike class, if we have enough entries, we would run a seperate class, so get your entries from.
http://www.enduro-neec.org.uk/