Can't say I've heard that story before. We've seen one or 2 examples where a 3 was stamped and then a 2 stamped over it. Being Brisbane built it should have XX7 or XU3 stamped on the plate to be a Sandman, no matter what.
Console bracket can be added and if it has a comfort pack then it will have the headlining teeth. Has it been restored?

Only definitive way to prove it's a Sandman would be to get the Holden Historical Services report. Sounds like a nice van either way