The Longbranch and Savage No4MkI* have a simplified bolt release cutout on the receiver. That reduced machining and parts for wartime expediency.
If your Savage No4MkI* has been upgraded to receiver mounted MkII trigger, it's is then a No4 MkI/3
Is your rifle marked as being FTR'd? Bore condition is everything for accuracy, most No4's well shoot 4 moa or better.
The early Savage and Longbranch No4's had MkI ladder sights (precision adjustment), later production had a flip battle sight. The longbranch and Savage sights are harder to find, many prefer them because they have a smaller peep hole.
Through the life of a typical Enfield it could end up with about any rear sight. Easy to replace, many like the No.5 Jungle Carbine 200 to 800 MkI sight because it has finer elevation adjustment.
The Parker-Hale 5C makes a great upgrade rear sight if you get serious about target work.
If the rifle has been FTR'd it can have just about any parts on it, ROF, BSA, LB, to name a few. It's not uncommon for completely original rifles from Savage or Longbranch to have each others small parts. The two factories where in close proximity, one in U.S. and other in Canada, they exchanged small parts as needed.