If it's chambered in 6.5x54MS then it's a model 1903 as only the 1903 was chambered in 6.5mm. The side mount is quite common. Now it's the makers name whigh has hed the holes drilled through it. Gesteyr Wabinfabriks or something similar. I am not well enough to go and pull the Steyrs out of storage to see. Depending on the year it was made the writing changed as the company changed it's name over the years.
Ahh I did a little searching on a Mannlicher forum and found this:-
Oesterreichische Waffenfabrik Gesellschaft, Steyr this is from 1905 and a Greek contract. Later it became Steyr Werke AG in 1930
Hope that helps a little.