Hi Wally,
Around 1994, give or take a year, I was involved in restoring that actual Honest John launcher vehicle at REME workshops for the RA's Rotunda Museum. The brakes were inoperative and a few mechanical jobs, recall the gear selectors were seized as well. Once running well I took it around our test area and it was a lovely sounding engine, glad I was not paying for the petrol. I recollect cleaning the carburettor and it was the size of a saucepan., It was then repainted and eventually went in to the Firepower museum. The axle width of the rear bogie was considerably wider than the front, which you had to be aware of. The supply truck was not so 'glamorous'.
Will have to dig out my photos of it when it was taken back to the Rotunda.
cheers Richard