stock disk marking identification on Lee Enfield 1904 Mark 1***

I have a Mark 1*** with the serial G 839, nosecap also G 839 and bolt G 837. This must have been a grenade launching rifle as there are faint marks on the rear handguard from the wire wrap. The fore-end is a replacement without any number and with the later fore-end pin without the washers, but has the complete volley sight.

The buttstock has been on this rifle for a long time as the bottom screw slot is worn down to the point where a screwdriver will not fit. Also note the early butt swivel bracket too.

Can anyone identify the disk marking ?