Hi Frank,
Yes, 'R' is spot on. Your engine is an ex-Francis Barnett 6E. It's no different mechanically from any other 6E. Villiers just had their own way of numbering their engines so they knew who they sold them to.
And "yes" to the other question but I'm from further south, deep in AFL territory.
Finally, you mention you have a four speed box. Technically these were never fitted to the 6E but I've seen it done. Apparently not quite as simple as expected but easy enough according to those who have done it.
Cheers,