Franco Oliano, who has already contributed a lot of material on Italian Machines, found this most interesting insight on a Jawa conversion and has kindly sent in some details and very interesting pictures.
Franco had found this material (that reveal the prototype of Mantovani's engine), inside an old issue of 'Moto Sprint'.
In 1979, Romano Mantovani (better known as 'Pipeta') from Bergantino (Italy), managed to operate a revolutionary type of speedway engine, following two years of testing. It was a conversion based on a 2 valve Jawa, with the head having a rotating valve. The timing system made use of an external chain, the movement was given to the rotating valve by means of a conical pair. This prototype had magneto ignition and could turn at about 9,000 rpm. The compression ratio was 18:1.
was planning to realize a new engine based on a 4 valve Jawa, in order
to get rid of the external chain, with electronic ignition.