Ok, so you are bottoming out on the inner face. L1A1 barrels use a breeching washer, unlike the "metric" barrels. I say that because even the metric barrels are 1x16.
Barrel threads are 1"x16 tpi, so you are actually where you want to be if not a little over for final torquing. Usually you want to be about 10:30. You measured you gap at .062. The threads are 16 per inch, so one thread = .0625. You are one turn out. So a breeching washer of .062-.065 is needed. Since the nominal breeching washers (1-8) (.565-.600) are still too small, you will need to either make up the rest with shims or have a specialty size made. One of the many problems with aftermarket receivers and/or barrels. I guess Aussie pattern receivers are known for this.
You also have the problem of hitting the inner face before you are timed, so you will have to take a couple of strokes with a file on the barrel face until it times closer to TDC. You do not want to back it out another turn as you will never find a locking shoulder that will work and you will have an unsupported case. You may be able to time it as is, but I would rather know for sure I am timing it on the barrel shoulder and not the inner face.
Gunplumber usually has this stuff for sale:
GunplumberGood luck!