Hi
Big question really.
MLE's have no stripper clip bridge, open rear sight, set up for 215gr bullets.
SMLE No.1 have stripper bridge, full nose cap with no barrel exposed.
No.4 have stripper bridge, aperture sight, exposed barrel at muzzle.
No.5 is the jungle carbine version of Mk4 with infamous wandering POI.
Lots of minor variations in the MK's (eg: 1,2,3,4,4* etc) like bolt releases and the way the trigger is slung.
The Indian Isaphore No.1's are the 12 shot .308's extra heat treated to handle the extra pressure.
Mine is a No.4 Mk2 made in 1955 and was one of the last. Shoots like a house on fire.