Lee Speed ...

Well I found a decent sporterized 1906 SMLE Mk.I*** without the charger bridge.  The finish is pretty good for a 100+ yr old rifle and the rifling still there.  Next step is to see if it'll shoot, and if so start the project.  I'm going to have the sights pulled and replaced with express sights (if I could find the Lee Speed express leaf/ladder sight, that would be awesome), then restock it with a Boyd's walnut stock with an ebony tip.

That is a rather scarce SMLE 'prototype'.  The other half of the charger bridge was mounted on the bolt head.  I see the sliding guide rail is still present on the bolt head on yours.   I have one and wanted a scope on it but did not want to alter it in any way so I glued a scope mount base on.  Mine has a seriously rust damaged bore but after fire-lapping and custom paper patched bullets, it actually shoots!  It won't win any competitions any time soon though.

That rear sight is a valuable piece. I paid $60 for the Watkins-Speed sight I picked up for my 1906 BSA/Sparkbrook Mk I***, and that was almost 3 years ago. If you want to know how to tear the sight apart for cleaning then search for topics by me, I did a thread on it quite some time ago. As to the serial number, the original serial was struck and the rifle renumbered when they were refurbed and sold to the Irish. The most common ones are ER and CR prefix rifles. The ER prefix rifles tend to retain Mk I parts while the CR prefix rifles tend to have been upgraded with Mk III parts. Of course many were sported after being sold out of service. Restoring one is quite difficult, as I can attest to.

We need a big warning sign, in red and flashing.

I agree completely, muffett. Makes ones heart kind of stop a moment. Nailcreek, here's a little trick of the trade. It is common for the butt stock bolt to be siezed. That is why lots of us use screwdrivers with a square shank. You put a small crescent wrench on the shank and it gives you enough extra leverage to loosen the bolt.

While I really do understand the "WARNING ENFIELD PURISTS DO NOT READ" comment, the rifle was "sporterized" when I purchased it.  At present, I've asked the g'smith to check the headspace and test fire it.  If it checks out, I do plan on moving forward with the project - but very carefully.  For example, the smith asked whether I wanted to grind down the charger rail - to which I said "no".  I realize we are just custodians of these items, and who knows ... someone, at some point may wish to try and restore it.