WVFRED:
I just looked at my1871, 1888, 1891, 1893, 1895, 1896. 1898, 1905, 1908,1922, 1924 Mausers.
I do believe this is an 1891 with the safety lever altered nicely and the Rigby style stiker "peep" sight.
The 1891 is a perfectly good action. They usually didn't come with an "in-stock" magazine. They had an extended straight line. But, like one of my 1888's, the rifle crafters did many great improvements or changes to the Sporting guns. I saw that Dons noted it as a .303(?). You noted it as a 7.65 Argintine. I assume this is the correct cartridge. Great one for hunting. Mine are very accurate.
What a great find.