I always found the "Light Horse" story behind these very dubious indeed.

Normal SMLES are perfectly fine for cavalry (and whole Divisions were equipped this way) - either slung or used from a bucket scabbard. I've tried it myself, using original equipment (RMP & RHA mounted units). The charger bridge in particular makes not the slightest difference to withdrawal from a scabbard, and its loss would have a significant detrimental impact on the combat use of the rifle. Lets not forget cavalry units were usually used as mobile infantry in both Palestine and the Western Front, and were expected to provide the same firepower as any other infantry.

To me, these modifications in fact resemble those on rifles to be issued to (unreliable) native troops - i.e. they have been deliberately partly de-milled by the deletion of the bayonet and charger bridge. I would guess that, if these rifles are any sort of semi-official modification - they were knocked up out of scrap parts in order to equip local levies or guards.

Some things on this particular rifle look fairly suspect in their own right. Can we have some close up shots of the volley sight plate, the Ishy screw, the finger grooves and the bolt number?