I owned a Whitworth .375H&H Mag for a while way back in the day. It was marked Interarms and Mark X. It had the Whitworth/Manchester and Made in Yugoslavia markings both. They used a standard commercial Yugo 98 action and opened both the magazine and the receiver to fit a .375 length cartridge. The gun was of what I would call average over the counter quality. The action could have used smoothing up some. It had a very nicely grained walnut stock with oil finish, but the cheek was sharp and thin and the whole rifle only weighed in the 7 .lbs range. Bucked like mule. Interarms did a lot of squirrely stuff in the 70's/80's as I remember it. They definitely put together many sporterized military rifles for sale here in the US on Pattern14/17, No.1s, No.4s, and Mausers.