During World War II Great Britain, Canada, and the United States manufactured variations of the SMLE No. 4 rifle. And Holland & Holland rendered a small number of No.4 Mk. Is into sniping/target rifles for extreme long-range accuracy.

1. No. 4 Mk. Is have a spring-loaded vertical interlock that need be used to allow its bolt head (and bolt) to be removed from the receiver while No.4 Mk. I*s use a simplified system that dispenses with the interlock assembly in favor of a rotating bolt head-with-slot. I am nearly certain that No.4 Mk. I*s are unable to use No.4 Mk. I bolt heads because the slot that allows bolt insertion and removal is absent. . . . BUT can No.4 Mk. Is accept and function correctly with No.4 Mk. I* bolt heads? Is the presence of its slot irrelevant for use in a receiver that allows bolt head to be manipulated by way of an interlock?

2. Holland & Holland created a small number of long-range No.4 Mk. I rifles. Did these rifles use [especially adjusted] military trigger assemblies, or did Holland & Holland use some sort of target/competition trigger that was designed to be adjustable? If the trigger was a military assembly, what was the result of 'smithing it - that is, weight of pull, creep, did it retain the "double-pull" feature, etc.? I've always believed that while standard military double-pull triggers can be "improved" by a gunsmith to become acceptable for most big game hunting, for precision a 500-800 yards, such improvement by gunsmith just wasn't possible.

3. Following up #2, since SMLEs as competition rifles have been in use for generations, it is likely that third-party match triggers have been made. Please identify adjustable target/competition trigger assemblies, also such trigger assemblies that can be installed on No.4 Mk. IIs.

4. Many years ago I read an article that described a simple, easy, inexpensive method to alter No.4 elevation-ONLY rear sight assemblies to allow some windage adjustment also. Of course I no longer have the article, nor do I remember the process described. I will appreciate information pertaining to how to render the sight assembly adjustable for windage and elevation.

5. Following up #4, please identify adjustable target/competition rear sight assemblies, preferably that are close to as compact and sturdy as the military assembly.

NO difference at all in the bolts; only the receivers on the *s do not have the plunger; just a slot in the bolt head guide. You need the slot in the bolt head and the receivers on both rifles. The slot is not "irrelevant"; quite necessary on both.
Triggers; I think they were just mil triggers but the preferred one is the #4MK2 receives which hinges the triggers off the receivers instead of the trigger guards; easier to maintain a consistent pull.
No match triggers that I know of.
Don't know about your sight question.

Hi. You should bear in mind that where the Lee Enfield was, mostly, used for target shooting it was done under rules that required the rifle to be used in its "as issued" state. That no modification was allowed.

More relaxed rules allowed packing or bedding of the barrel and target sights providing more precise changes of MPI. But the as issued triggers have always been good enough "as issued" although on the No 4 Mk 2 and the Mk 3 (essentially an No 4 Mk 1* modified to Mk 2 configuration - I believe) the trigger was hung from the receiver and not the trigger guard.

Holland's essentially took the most accurate rifles from a particular batch and altered them as sniper rifles. They did not "make up" from component barrel and receiver such rifles.

One "made up" target version of the SMLE did however use thicker barrels. Such that the handguard had to be relieved and the nose cap hole enlarged. These were popular in Australia and some of these were set up as sniper weapons.

I am unaware of ANY specific target rifles on the SMLE or No4 ever being made by Holland's. A J Parker, Parker Hale, Fulton and Alex Martin certainly...but Holland' never.

Hope it helps.

The backsight modification was to fit a shoe type over the military aperture and this auxiliary aperture on top of the existing military sight then gave limited windage adjustment.

I think it is the 8/53 catalogue sight or maybe I am cofusing it withe the No 8 backsight...but will stand corrected. They now fetch a lot of money! Certainly there was a shoe arrangement that did fit over the standard No 4 backsight.