Hi to anyone interested in this subject.
Unfortunatly I cannot answer the question of "how many were made"as I have been told some were sold as complete engines and some as kits to put onto single
OHC bottem ends.Near the engine number on the DS crankcase the history of the bottem end can be found,with "DOHC" or "PLPS" appearing to relate to the twin cams.I may be wrong but the engine numbers seem to be continuous ,irrespective of type,as was the historic system used by so many manufacturers.
I am in the UK East Midlands,and I know of 3 DOHC Weslakes,all 500cc,one of which was used by Reg Wilson in a [Gordon May] Comet frame at Sheffield.These engines are terrible to work on,but Dave Jessup once said he had a works bike which was fantastic on the track until it went back for a service after which it was "ordinary".I suspect they lost the cam timings!