If there is no gunsmith mark somewhere on it, like ARS or AZEX (and others) then there is no way to tell. However, if it is a foreign receiver, chances are pretty good it can be made to run just fine. The two problems are generally the crappy two-piece gas piston and the "unibrow" feed ramps. If it is an import, then the feed ramp will correct and not the "unibrow." Then it is a simple matter of changing out the gas piston.
The other thing to remember, though, is that many Century builds require US floorplates and followers to remain legal. Otherwise, you'll have to change out some other parts to use any mag. This is particularly so with the L1A1 derivatives.
Ash