John is riht, of course.
This started off as a (long) Magazine Lee-Enfield Rifle mark I* in 1900. When the SMLE came in it was converted to SMLE status as a Converted Mark IV and then it was later converted to .22" bore for use as a training rifle.
NICE catch!
The Buttstock Markings give us a great deal of THIS rifle's history. Can you post a clearer close-up of these or, better yet, give us a transcript of what is there? I am sure that someone here will be able to put the tale together.
Sparkbrook built numbers of LEIs and LEI*s and then VERY small numbers of the first SMLEs. They are said to have built a TINY number of SMLE Mark III rifles very early in 1907, but that would have been under BSA administration. The Government sold the plant to BSA in 1906, after which it was used to make a few spare parts and then closed down. It was seized BACK by the Government when it became obvious that the Great War was going to last more than a couple of months, re-opened yet again and operated as Birmingham Repair Factory until the end of the War.
As Birmingham Repair, its inspectorate punches used a SCRIPT (slanted) letter "B" over the Inspector number; BSA used a ROMAN (upright) "B" over the Inspector number.
Hope this helps.