![Embarrassed :oops:](./images/smilies/icon_redface.gif)
The conversion looks like it is one done by J. P. Wilson the County refurbishers, as it is identical to the one in the picture below of their demonstrator, with the crane mounted mid-way along the cab, the roof design where the lights are, and the long mudguards with operator entry at the back. I was led to believe that they made only one.
Jones used a cab that looked like a Duncan (I think it may have even used Duncan doors) with a large RHS frame from the axle incorporated at the back edge for the crane. The branch diverters would have been from the cab right out to the front too, but they often got damaged and replaced with whatever was to hand.
Chieftain Forge's crane cab looked like it was cut from solid plate, and had the distinction of being the only cab ever tested by the NIAE that was still completely undamaged after the tests and fit for sale!
The slew cylinders on that one are in fact at the bottom of the column, as it's a short-column crane and the column stops at them on the cab roof.
Dave. S.