UK based professional model maker David Provan sells a number of kits, one of which is the early 4 wheel version of SR&RL Railbus #4.
The picture below shows the photo-etch fret;-
And the picture below shows the various cast parts;-
David showed his own made up model at the November 2010 meet of the UK Slim Gauge Circle at Bilton;-
A roof off view showing a view of the motor and 2 stage gearbox supplied in the kit (to be assembled by the modeller);-
An underside view of the drive, shown here on David’s pilot model of his new kit for the 4 wheel pilot truck version of this kit;-
David’s flyer announcing the new 4 wheel pilot truck version of this kit;-
Update: 7th November 2013: David had this kit on sale at the recent Hillmorton meet of the UK Slim Gauge Circle.