So a bit of an update...
Got the rifle in. It's a Canadian issue SMLE, and since I bought it in Canada, solid chance this is where it last saw service too. No import or export marks on it, no ENGLAND stamps or british commercial proof marks.
This is the reinforcing bolt I took out of the sporterized forestock. It's not a hardware store screw or bolt, looks to be purpose-made as a stock reinforcing bolt. It's blued, and the "nut" is shouldered.
Here's a shot of the inletting in the forestock for it, which is square bottomed (i.e. it was machined to have a flat bottom, not just counter-sunk with a drill bit like bubba would do. Both sides are similar.
The barelled action is a bit of a conundrum, really. It is clearly a low miles gun, and had never been refinished - the inside of the receiver was still n the white from the original factory rust blue job. Bore is nice, does not close on a SAAMI NOGO. Even and good locking recess contact. The only thing I could find wrong with it is the bolt would sometimes not close - the upper lip of the bolt face would catch maybe 1 in 5 times cycling the action - a couple thou of overlap on the front of the receiver ring was all that was hanging it up, surprisingly. I looked at a half dozen other SMLEs in my rack, and the receivers all had a slight chamfer there, where the bolt head is supposed to slip under and into the front receiver ring. This one did not have that - like it missed a machining or hand finishing step at the factory. Makes me wonder if that is why it got EY stamped, as I could not find anything else wrong with it - and I have the gauges to check for the most part. I very slightly broke that edge with a small half round file, and now the gun cycles 100% reliably.
Then I set about addressing the missing charger bridge. Luckily I had another thrashed 1918 SSA barelled action that was badly pitted sitting here, so it has donated its charger bridge. Machined new rivets on the lathe, flared one end in a rivet mandrel and installed the new bridge. I build an inner anvil in the mill from some scrap stock (nothing fancy, just a correct thickness block of mild steel) to fit inside the magazine recess so I could support the receiver on an anvil, and then riveted over the rivet heads with a ball peen. Dressed flush with a file, sanded to 400, and then rust blued the bridge (it had all its finish gone) to match the rust blue finish on the rest of the receiver. I think it turned out acceptably.
I'll re-assemble with the stock set from that ratty SSA I have here (the one that donated its receiver bridge) and post some pics later. I made a couple minor wood repairs to that stock, but otherwise it's a nice late WW1 walnut stock set. Wearing a nice steel buttplate with brass trap, SSA trigger guard, blued steel unit disk.
Now I have to decide wheather to re-install the re-inforcing bolt from the sporterized stock or not. There is no evidence the sporterized rifle was wire wrapped behind the rear sight, but I suspect it likely was up behind the nose cap, given the re-inforcing bolt. Need to decide whether I put the re-inforcing bolt in this other stock set and wrap the forestock up by the nose cap or not.
FWIW, this EY rifle was all matching in terms of what was there. Bolt, barrel, receiver, rear sight. Pretty sure it was never FTR.