I think you are right about Sam Cummings Interarms and the Interarms warehouse in the Dawsen street in Manchester. there can be no doubt that Interarms owns Whitworth than and with Cummings connections everywhere it was this firm in the end making and trading sporting rifles in the US and other countrys.

remember seeing a dokumentary film about Cummings and his warehouse stocked with guns when I was a boy. it was impressive when he was shooting a german MG 42 he had collect in the Normandy in 1946 on the indoor range in the basement of this house.
Cummings was very intelligent but absolutly stingy and never throw anything away. Interarms was probably the reincarnation of the old Bannermanns warehouse and used anything or wait for the moment it can be used again.