As above, chassis came blank. I've had a WB tonner with one, and a friend actually bought a brand new one in 1988-9. He bought it with a receipt from the GMH dealer as a HQ chassis (it was a WB one) to put under a HQ tonner cab. When you went to register them you had to go via the Police who'd check it out and issue you with a number to get stamped onto the rail by an accredited place (usually the blue-slip issuer). Number too the form (using NSW as an example):

NyyxxxxP. N is NSW, yy is the year, xxxx is a sequential number for engine or chassis numbers issued in the State for that year, and P means Police.