Ditto Wild Cattles responses.
Crawford & Whatley in their "History of W&C Scott Gunmakers" tell us W&S introduced the Proprietary Hammerless in 1900 and that more than any other W&S models these were largely machine produced -- on "the interchangeable principle." They also tell us these were "fitted with the Webley Screw Grip ..." (p 69). As illustrated, these obviously have the straight stepped top-extension variant.
The older A&W screwgrip boxlocks (p. 21 of catalog) were somewhat more expensive and distinguished by intercepting sears in the better grades and I suspect most have the doll's head variant top-extension. On page 28 of the 1914 catalog there is a double-rifle variant so illustrated. Lots of W. Evans screw-grip boxlocks have these interceptors.
Most of the W&R screw-grip sidelocks I've come across have the doll's head variant.
