The 57 means that it was made by Arrieta. The 03 means that it was a shotgun. The 85 means that it was the 85th action serial numbered that year and the 96 means that it was made in 1996.
Arrieta guns do not have the model listed on the gun but you can probably determine it from the number of pins (5 or 7) and the style of the engraving as compared to the descriptions in the Blue Book.

Bob Beach