Just put myself out of misery -This is an officer’s MKii horseshoe case with frog for sword scabbard sewn onThe sword frog attachment for officers was first introduced in 1901/ 1902…MKII This was a conversion of the MKI case by sewing on a frog.
The MKI case without frog would not have had the horizontal steadying strap. MKII has a steadying strap as does the MKIII. Both MKI and MKII had a single strap and buckle for securing to the saddle.
MKIII differed from MKII in having 2 straps and buckles for attaching to the saddle dees. Necessary for attaching to the MKIV saddle with the pair these on each side.