This ones been on e bay a couple of times and failed to find a buyer so far...Though a friend of mine has made an offer on it...
It's an interesting historical piece and I admit I get tempted myself...
I rebuilt one of these motors a while back and although it looks good it's no Gold Star...However, it does have potential with a bit of reworking...
The piston is an odd one peculiar to the engine due to the limitations of fitting an OHV top end to a standard M20 bottom end...
There are also other design features that would benefit from rethinking as well..Ian
email (option): ian@wright52.plus.com
I took this photo at the Stafford classic bike show a few years ago the bike was for sale in the outside auto jumble,I think it was up for sale at £3000 but may be wrong,I was at yoemans motorcycles the other day and there is an engine from one of these,its a late bottom end six figure number. 
That bike was £5000 at the time and being sold by an Italian who bought over mainly Japanese bikes from Italy to sell....
I first saw it before Stafford, at Festival of a Thousand Bikes at Brands Hatch...
I'd have bought it at both venues had the chap been prepared to come down to a reasonable price but he wouldn't...At the time it was a very high price bearing in mind that it was a long time ago,it didn't run and had no dynamo internals!...
As well as the interesting engine I liked the Guzzi type swinging arm suspension fitted to that example...
The engine at George Yeomans is the one from the recent e bay advert and is for sale if anyone fancies an interesting project...Ian...
email (option): ian@wright52.plus.com