"Sharps firearms" by Frank Sellers, a fine source.
Reciever markings on an 1874 after August 1875 but model 1859 and early 1874
SHARPS' RIFLE CO. C. Sharps' PAT.
PAT. APR 6, 1869 SEPT. 12th 1848
Then there's the lock plate, barrel, rear sight and small parts depending on model and year of manufacture.