however the brass ring on the stock is something that I've only seen on older designs like the RIC carbines and and number 1 rifles. I would wager that this is just a parts rifle, assembled from a huge stack of parts and cut down since there is little collectors value in it.
I did not notice the regimental disc. You are correct that this disc was not a feature of the No.4 rifle, or later production No.1 SMLE rifles. The disc was discontinued when it was found that German military intelligence was using the discs from captured rifles to keep track of which British regiments were on which section of the front at anyone time.
I have seen a SMLE MkI buttstock (the early type of English Walnut with extra lightening tunnels drilled under the butt plate) fitted to a no.4, how it got there is unknown. The butts aren't entirely interchangable, but are easily fitted to the other type action bodies. Some butts made specifically to be used with either type rifle without alteration were manufactured during WW2.
While throat erosion is the most common damage to Enfield bores due to hard use, damage to the crown and rifling within several inches of the muzzle is nearly as common, and due entirely to improper cleaning practices.
It was said that a recruit who did not know how to handle the pull through could do more damage to the bore in five minutes than decades of service with tens of thousands of rounds fired.
I've run across more than a few otherwise very nice bores with the crown worn into a lop sided oval and little or no rifling for the last six inches. This comes from dragging a grit laden pull through out the muzzle without making sure to pull the cord straight out. The occasional use of jointed steel cleaning rods by third world users does even more damage.
Then only a inch or so of the rifling at the muzzle is damaged counter boring can save the barrel, if damage extends further back cutting the barrel back is often the only way to obtain useful accuracy.
Fore ends damaged in bayonet practice are fairly common, and one may find one dirt cheap in a smith's parts bin.
If one wishes to build a snub nosed Tanker or Bulldog as a knockaround beater they should start with a pre-disastered barrel and a fore end thats ready for the scrap pile.
If one wishes to build a shorty with bayonet lugs and sight locator lugs intact, you can turn down the cut down barrel's muzzle then bore out the chopped off muzzle section to a slip fit and silver solder in place.
This can also be done if fitting a custom tightbore barrel, to preserve the original configuration.
High Force 44 is the best silver solder for this sort of work.