SR Griffin / Kornbrath is my vote. Im fairly certain Ive seen that bison in Kornbrath catalogs or rifles attributed to him. I know, I know, theyre all Kornbrath...

Im 95% on SRG. Checkering pattern is known, the rounded bottom of the stock adjacent to the floorplate, no cheek piece, overall shape of the butt especially the comb nose, long forend. Little doubt.

There were several early SRG stocked rifles that had Pope barrels. Pope liked them long and could certainly do 27. Not sure who else was making anything longer than 26? On a Pope barrel there was an unusually long straight section just in front of the receiver. This one isnt Exactly the same, but its not the standard contour either.

Take a look at Dans SRG / Pope on another thread

I think its was on the low side of retail if thats what it is.