Scanning through the online photograph archives for the City of Vancouver, BC, Canada, there were a pair of photos showing a circular "railway" used to mount drilling and boring machines for preparing very large "Scotch Marine Boilers" for industrial service. Here are links to the two photos:
You can see two boilers in the background of the first photo. Note how the units are individually connected to electricity by an overhead "extension cord".
You could easily see these units as self-propelled versions, possibly with side tracks to store unused equipment, or another unit with a scaffold for painting or otherwise finishing the boiler.
The prototype appears to be approximately 36" gauge, but there is no logical reason why a minimum gauge version couldn't be considered if it was designed properly.
Searching through the archives with the keyword "machinery" will show you several other photos of these machine shops and boilers.
I hope this inspires someone to create their own little boiler works.