NRAManual on Lee Enfields
The DND Manual looks great! I wish it had been available to me in the early 1990's when I undertook a similar project to this one in order to compete in our New Ontario Shooters' Association shooters version of Military Rifle matches at the Mt McKay 500 yard Range at the Lakehead/Thunder Bay.
In the spirit of the Match some modifications were allowed as to glass bedding and reinforcing the trigger guard of the No. 4 Mk I *.
At that time I had acquired two absolutely mint 1950 and 51 Korean War era Long Branch No. 4 Mk I's I selected one to glass bed and left the other completely stock. The latter I later shot at Connaught in 1998 at CFSAC and again in the 2001 version of the DCRA APM Historical Military Rifle Matches at Connaught Ranges. Ten shots on score at Fig 11 at 300 metres with issue sling.
This said, I would recommend as well the NRA Manual for glass bedding the No. 4 for target work while keeping the exterior totally stock appearing. Kinda like a stock Dodge from the 1960's with either a 440 Hemi or 383 under the hood as the improved bedding will help you shoot at least five shot inch and a half groups measured to the outside of the bullet holes at 100 yards. At least that is what I was able to achieve with my NRA manual glass bedded No. 4.
Essentially you need to achieve at least five shot 2" inch groups at 100 yards or 100 metres so that at 300 yards/300 metres the groups will stay on the Fig II Target centre as good as you can hold with iron sights. At 300 yards your optimum 2" groups shot with an ISSUE web sling from prone will now be 6" or better.
I would recommend using mismatched or "beater grade" rifles for glass bedding or modifications. The NRA Excellent No. 4 from 1990 costing $179.00 from Districorp at that time would now be worth about $600 or better..maybe more.
I would recommend having a side mount installed on your No 4 for a Central sight for testing handloads versus the PH sight which is heavy and costs as much as the rifle. The Central sight is also easier to acquire or use in my opinion. Then in the Historical Military Rifle you can just take it off. without any major alteration being present.
Hope your No 4 has a milled ladder sight verus the pressed metal one.