Tim, is the serial number the only marking on the gun? I doubt it. Pics, or at least accurate verbal description of ALL the markings as well as pics of the gun in general can tell a lot. Something as simple as the proof marks can tell where the gun was manufactured, and hence whether it is a Mark-X or not. You will have to remove the barreled action from the stock to find all the markings on the rifle.

Interarms was primarily an importer as opposed to a manufacturer, and while the Zastava built Mauser Mark-X rifle was the most frequently found, they did import other makes. The Zastava built Mauser 98 pattern rifles were quality made. I have owned several over the years, and liked them. I now have a Mitchell Arms imported Zastava Mark-X in 30-06 that I picked up on the cheap. It is beautifully fit and finished, and I do believe has a 338-06 rechambering / reboring in its future.

Larry