The choke tubes supplied with Red Label shotguns were flush, your's sound like aftermarket extended chokes. During the 1991 era there were 2 different choke types, the original Win-choke types (which will be indicated by a SIC suffix on the box end label or Ruger Letter), and the subsequent Briley type (which will be indicated by SC suffix on the box end label or Ruger Letter). However, during the transition period (approximately 1988-to-1994) there were many different variations, not all of them were noted in RENE collectors Guide. So...with Ruger, never say never.
So check the chokes for any markings that indicate a manufacturers name, check the box end marking, and get a letter from Ruger records.