Wow, I hate to say it, but that looks like it could possibly be an original SA crown - certainly isn't a hacksaw job, and the surface shows age. If so, it was a very unfortunate and/or unlucky choice by the party who modified it. Check out the home page to see the current list of known 26" barreled rifle numbers.

I actually have found two of the BoOF rifles.

My first (388786) came with a 1902C sight, in an un-marked M1899-length carbine stock. This is not the classic/original "book" configuration, but does match the one in the SA Museum. I do not find it completely unreasonable to speculate that - while under test to see if one arm would be acceptable to all branches - some may have been fitted with carbine stocks.

My second (389182) came in a properly dated (JSA/1902) rifle stock - which I'm sure is the original - but sadly was chopped just ahead of the band. BUT, it did still have the special sights (an M1901 hand-graduated to 2100 yds, and front blade with a VERY slightly different height/curvature). The original stocks were made new for the test guns and lacked the final lightening slot.