Arrived home safely.
Departed Loxton at 07:30, arrived home (after 740km) at 17:45.
Several
'Canine Comfort Stops', driver changeovers & a lunch-break along the way.
En route, I received a call from the bloque who imported the Chevy Workhorse chassis for Winnebago/Avida.
He said the lower wishbones were no longer available, and I'd have to have one made. He also opined that a probable cause is people inflating the front airbags to 100psi. I assured him that the previous owner recommended no more than 50~60psi, a recommendation I have followed.
I updated him with the info that the mechanic who spotted Girt's problem had been searching the internet, and found a US supplier... who was out of stock.

But plans a production run in
three months.
He was surprised, but pleased.
His solution was to have the wishbone pushed back into alignment, welded & plated. He says others with this problem have done this, and had no issues with roadworthy certification.
I still suspect the railways attempt to hold it down. If they dogged it down without air & then started the motor prior to un-tying it in Adelaide it would have built up air & ????? oooops!
[Bruce, the airbags are independent of the motor... no air brakes etc., just valved air lines (which I had installed) running from the airbags to a convenient point in the engine bay so I don't have to lie under Girt to check/adjust air pressures.]
As Girt is safely ensconced in John's big shed
(thanks John!), I plan to contact the US supplier and determine exactly
when he will be making the wishbones, cost thereof, and cost to airfreight to Oz.
Armed with these details, I will then consult our nearest VicRoads Roadworthy Inspection person and check if the Victorian colony agrees with its northern neighbour's attitude to a repaired
(rather than replaced) suspension component.
Only then will I be in a position to make an informed decision on how to proceed... even if in means waiting three months to see Girt mobile again.
At least there is now the hope that I will
not be left with an unrepairable $100,000+ pile of scrap.