G'day,
Sorry I've been away and missed this post.
You have an Aussie SMLE which has been surplussed after the war and converted into a target-shooter's range rifle. The rifle itself is a pretty common garden-variety Lithgow No1. The receiver was made in 1942 but the rifle was completed and stocked up in 1943. Pretty common to have a later date on the buttstock than the one on the receiver.
The full-length top wood is a popular postwar modification. As target shooters used peepsights like the one fitted to your rifle, there was no need for the military rearsight. As the standard military wood was comprised of a front and a rear handguard, removing the rearsight, rearsight mount and sight protector left a big open space. To stop heat haze changing the sight picture, one-piece top woods were popular.
It is possible that your rifle has been rebarreled with a heavy barrel. These were popular for target shooters, and are a 25.5inch barrel which uses the heavier profile of the earlier Long Lee barrel of 30.2 inches, just at the shorter length for better accuracy.
As No4MkI(T) said, if the knox form (flat part just forward of where the barrel screws into the receiver) has a capital H stamped into it, then that shows it is a heavy barrel. These were often fitted after the war.
The HV refers to the higher velocity MkVII round. Early rifles were sighted to suit the round-nosed MkVI round, but when the MkVII round appeared around 1911, rifles had to have their rear sight beds modified slightly as the new round was of a higher velocity.
For some obscure reason, Aussie rifles were marked on the buttstock with HV, even decades after the MkVII round became the norm.
Nice rifle, you could return it to military trim with a bit of work, or keep it as-is for range shooting.
Cheers,
Matt