It would certainly seem more sensible to modify the frame to make the boiler fit rather than waffle around for another 5 years with nothing at all.
As I understand it, no change would have been required to the frame.
Apparently the front tubeplate sat at an angle to its intended position, and could not be bolted up to the existing smokebox. I would have thought that manufacturing a new smokebox to match the boiler would have been a fairly easy task, and all this would have been hidden from sight by the boiler cladding.
I'm told that the boiler does not meet Australian Standards.
It may have been possible to get an exemption from some Australian Standards since the boiler presumably met the standards required in Germany, and would have been pressure tested and steam tested in Germany and the appropriate documentation would have been available.
The manufacturer apparently agreed that some firebox stays did not meet the appropriate standard, and all of these were replaced at their cost when the boiler was returned to Germany.
The boiler of Tornado had similar problems with stays, and that boiler was returned to Germany twice for replacement of stays. But the locomotive ran many miles with the boiler as originally supplied, and I'm sure 3801 could have done so too.
We are not talking about nuclear physics here.
The German boiler was clearly more "rough and ready" than was expected here.
But it worked as a boiler and passed the required tests.
I suspect the problem was that the customer said "It isn't what we wanted"
and the manufacturer said "it is exactly what you asked for".
When the boiler was returned to Germany, there were statements made that the Germans would have to build a new boiler since the one supplied was unsatisfactory.
Clearly this didn't happen, so the boiler must have been built to the specification provided.
I note that one feature of "Tornado" was that all the drawings involved including those of the boiler, were redrawn to current standards.
I'm fairly sure this wasn't done for 3801 and this might have been a good idea.
But since there was to be no new boiler without more money being paid, the whole "Return to Germany" operation became a bigger embarrassment and nobody wanted to say anything.
But if 3801's boiler was easier to fix than the new boiler, that would always have been the case and could have been done ten years ago.