From George Moller, American Military Shoulder Arms, Vol III, and Reilly, U.S. Military small arms 1816-1865 you will find;
L,G & Y "special contract 1861" rifle muskets look like a Colt "special" because they got their machines and specs from Colt.
They delivered 50,020 guns on a contract for 50,000. 5000 delivered in 1862, 24,200 in 1863 and 21,000 in 1865, completing their contract. **Also included on this "special 1861 contract", were Colt(100,005) and Amoskeag (27,001}
The date in the photo is 1863. The rod is of the correct pattern. It is the second type lock plate with the Eagle forward of the hammer. Reverse the lock screws and it will fit better... they're not the same length.
L. G. & Y was the successor of Robbins & Lawrence and following completion of the special 1861 contract continued as E. G. Lamson & Company making Palmer carbines.