Very nice acquisition, sir!
You have a commercial MLM Mk II. I have one similiar, but on the wrist, its marked "LSA" over "II". Mine also has the "for cordite only" notification in the same place too. That number appears to be a registry number for target shooting. I can make out "Lithgow" on your barrell, so good possibility it had the wrist markings scrubbed by a target shooter when the barrel was swapped. Speculation on my part, but this is something that shows up with some frequency on this board.
Cant help you with the date. The one in the know about these commercial guns is jc5. He's on here from time to time. You might try PM'ing him.
Again, very nice addition!