Even before the turn-of-the-century U.S. Live Bird and Inanimate Target competitors specified dimensions very similar to those used today
In 1887, Parker Representative W.S. Perry ordered a C Grade 10g with a LOP of 14 3/8" and DAC 1 1/4 X DAH 2 (Courtesy of Bill Murphy)
The Art of Wing Shooting: A Practical Treatise on the Use of the Shotgun ...William Bruce Leffingwell, 1895
http://books.google.com/books?id=e34EmE3tkfkC 'Capt.' John L. Brewer of Philadelphia.
A gun for pigeon shooting should weigh from 7 1/2 to anywhere under 8 pounds. It should be heavy at the breech, with a long and very straight stock, having a drop from 2 to 2 1/2 inches at the butt. These straight stocks are desirable, because they cause one to shoot high, something which is essential, as there is a tendency to undershoot, and nearly every pigeon is missed by shooting under or behind.
Fred Gilbert (1865-1928) was one of the worlds best known shooters from 1895-1915 and used a L.C. Smith to win the DuPont Worlds Pigeon Shooting Championship in 1895 and the E.C. Inanimate Target Championship Cup in 1896. The Fred Gilbert Specifications were for a drop at comb of 1 3/8 inches; at the heel, 2 inches; length from trigger to heel, 14 1/4 inches; trigger to toe 14 1/2 inches; and trigger to center of butt 14 inches; with a full pistol grip and 30-inch full choke barrels.
In Feb. 1898, C.W. Budd received on consignment a Parker $400 AAH Pigeon Gun SN 87449 with 30 Whitworth barrels F/F and 2 7/8 chambers. LOP was 14 and DAH 2 1/4 with a pistol grip stock and no safety. It weighed 7# 12 oz.
Lots more here, including the dimensions used by 28 competitors at a shoot in 1901
https://docs.google.com/document/d/1c7UkkNyMTZ9NAztILpzjSLKvgIneAw5i7eqkZ3d3Eno/preview re: the OPs guns, it is quite possible the pigeons are simply embellishment on a game gun, with dimensions as desired by the purchaser
