Books is correct. The differences are usually internal and very subtle. The first type is the Navy M1889, in 1892 that Army adopted it with wood grips instead of hard rubber. You may see an extra pin or screw here and there but the only REAL difference in that in 1901 they started adding lanyard rings. Many M1892's, M1894, M1896's had lanyard rings added later and many of these arms were sent back in 1918 and completely reworked as much as possible (like my M1901 for sale). The date of my M1896's serial number range (1901) makes me suspect it had the lanyard ring added before it left factory.
I have pattern 1872 cavalry sabers and artillery cannons right now for IWP. Sorry, no engineer, but will keep an eye open.
Chris Fischer
F Troop Company