RidgeRunner, I notice your original question was never answered. Doodlebugs were used by many railroads to haul trailers, passenger or freight...
They are indeed! 4807 and 4490 are part of the NSW Rail Transport Museum's diesel fleet. I'm probably biased, but I reckon 44's are much better...
Sten, I'm assuming you work for CityRail, what's your depot? I'm at Waterfall. Cheers, Mark.
To add to my previous post, here is a site that lists 30" gauge railroads around the world http://www.pearcedale.com/c&b/clasig.html
The only A-1-A + A-1-A Alcos here were the NSWGR 40 class locos.
I notice no-one ever actually answered your original question - On3 represents 36" or 3' gauge track, On30 represents 30" or 2'6" gauge track....