Hi Duncan my catalogue is out of date and the one you need 335 has been discontinued and the one in your photo is the 335a 2 way that's the only one they do now sorry about that. Chris.
The J2 switch on the top of the fuel tank (available from S&V?) is almost identical to the D/F original - only trouble is it is chromed and expensive but is a direct replacement. See Dispatch 65 for picture!