It does seem like a lot of work to make a repro L4 A whatever it now is! Especially that bathtub shaped lightening recess at the front of the magazine housing (see it.....? just to the front of the magazine, down...., on the top of the body...). That was another initial stumbling block that caused all manner of confusion when formulating the Mk3's to standardised L4A2 spec. Because the magazine was moved further forwards and the opening opened out to boot, unless the milling process used to cut the magazine lug recess was precisely central and mechanically prevented from deviating left or right by more than a gnats knacker, it would break out into that recess.
Even got a lightened Mk3/L4 butt slide. Top photo, looks like the body has been eating into sides of the butt during recoil buffering
That sling attached to the rear sling swivel was another bane of Armourrers lives too. It used to chew the recess up until it couldn't be made good anymore. No repair was suitable so plenty of butts were scrapped! The very best was the sling loop modification where a loop was welded to the top of the butt plate. Problem solved forever
Sorry...., getting into Bren train spotting mode a bit now so better shut up so nobody thinks I collect webbing and oil bottles too!