-JdK- This is Alec Pratt on his dirt track motorcycle at Kilbirnie stadium (Wellington, New Zealand) in November 1930. The engine is a late 1920s OHV Norton. The frame doesn't look like the Model DT frames. (Photo from The National Library of new Zealand).
-Steve- The Norton engine has been fitted into a 350cc Harley Peashooter frame of around 1928 vintage; see above.