Interesting info & supposition.
Indeed, the pistol grip, side-swing scope mounts & buttplate were added in the 1960s. The buttplate pushes the LOP out to 37.5cm. But the worn preliminary datastring for the 22 tube looks to read >>5.0<<. The 24 X 24 tubes have seen quite a bit of use. For all the 24 tubes, the original custodian must have been pushing something other than shot.
It may have been that of a Lady but the 24 X 24 tubeset had a sighting system and it doesn't look to have an odd rifling or such. And it looks to have been removed possibly in the modification as the purpose for the sighting system had passed. Plus the weight of both tubesets are somewhat close to proof.
Although not an impossibility, but has anyone heard of a two-barrel set ordered by a Lady during WWI?
Hochachtungsvoll,
Raimey
rse