Here are some pictures of Argentine Carbines showing differences between them.
Argentine receivers 1891
A view of the receivers on the 1891 Engineer's Carbine. I have two 1909 Carbines that have similar differences!!
Argentine 1909 Carbine
A view of the receivers and factory markings on the 1909 Carbines.
This shows a difference between the two 1909 carbines viewed from the muzzle. The 1891's all look the
same without the counter bored muzzle.