The usb dongle arrived this week and in a couple of days I will go to work and get the laptop and start hacking...

Regarding the tire size etc, Freightliner did the checks for engine, transmission, diff & wheel/tire and said its all correct.
Next door neighbour works for a local company that repairs speedo's etc.
Said to bring it in but havent had time yet.

On tyre size, I think the tyres/wheels are too small for my needs.
I put a towbar on the van and I am doing a lot of driveway "adjustments" now. Even been hung up a few times. Wheel spinning to get over the bump.
Think I may get airbags fitted so I can adjust height as I need. :-)

Ray