Page 10 of the shooters handbook:
SHOTGUN GAUGES
• Side-by-side, single shot, and lever action shotguns must be centerfire of at least 20 gauge and no larger the 10 gauge.
• Slide action shotguns must be centerfire of at least 16 gauge and no larger than 12 gauge.
• Side-by-side, single shot, and lever action centerfire shotguns in .410 are allowed within the Buckaroo Category only.
And the previous paragraph says:
Any side-by-side or single shot shotgun typical of the period from approximately 1860 until 1899 with or without external hammers, having single or double triggers is allowed. Automatic ejectors are allowed on single shot break action, lever, and pump action shotguns ONLY. Side- by-side shotguns may not use automatic ejectors. Lever action, tubular feed, exposed hammer shotguns of the period are allowed, whether original or replicas. The only slide action shotgun allowed is the Model 1897 Winchester shotgun, whether original or replica. Certain shooting categories require a specific type of shotgun and ammunition to be used. Military configurations are not allowed (i.e., trench guns). Please see the shooting categories for further information.
So it appears the "97", "original or replica" is approved,