Great looking model 17, chopper-just got a 26" modified barrel off of Ebay, to go with the 21" original barrel I had choked by Baker, back in the day. My 17 is checkered, but, a bit more used then yours. Not sure I'd ever need a 28 full choke tube, but, I would guess that was what my gun came with when new-had a Cutts on it, when I got it.
Best,
Ted