When you ordered a Fox SXS back in the day....you could order it with whatever chokes you wanted....pair of Skeet, pair of Mod, IC - Mod....whatever..../ and sometimes guys, over the years have "honed" them out if they were too tight for what they wanted...so chokes are hard to tell in my experience.
Just as a note - make darn sure the chambers are 2 3/4" ...remember a shotshell is measured - at firend length .../ don't just drop a 2 3/4" shell in there and since it fits you think you're ok. I don't remember for sure ...but I think there were some 2 1/2" chambers out there too in the older Fox's.../ if its not marked, be careful.
But find someone at your local club that knows the Fox guns better than I do ....and he can help you look at the gun to see where it should be marked.
The only way to tell how much restriction you have vs the bore diameter...is to use a real bore gague ...not those things you drop into the barrel from the muzzle end..( they can be off a lot )...or just go shoot it at a pattern board...and measure the pattern at 20 yds and see what you have...