Definitely not a real loco. The only Garretts the NSWGR ever had were the AD60s
The rather fuzzy label does say "proposed loco" and a date which can';t be read but may be 193x
Sounds like a mock up of what might have been if the NSWGR had gone with the idea of an express Garrett instead of building the C38 Pacifics . The class number's a bit of a giveaway - AC38 would have meant the locos being numbered in the 38xx block , where they would have clashed with the real C38s.... Buffer beam seems to show 3801 , which in the real world is the streamline C38 class leader
I don't know whether it bears a lot of resemblance to the Garrett proposal or whether that got as far as a GA (To be honest dirty snowball's posting was the first time I'd heard about the Garrett idea) . Looks like someone has taken the semi -streamline styling of the first 10 C38s and applied it to a notional Garrett
The model's 7mm by the look of it