Looking over the 2 stroke/4 stroke post. What 4 stroke motor would John Penton have used in 1968 if he was building a 4 stroke dirt bike? Would he have bought the Gilera 175 or Laverda 175 4 stroke motors to put in the KTM frame? The NSU motor was out of production in 1968. This might be an interestding project for some one with a steel tanker frame.
Jeff Borer combined two of JP's passions when he put an NSU engine in a Penton frame.
There is a photo of the bike in the gallery section @ 05 POG/KTM Day At The AMA Museum image #64.
Jack