357Mag accessory barrels have always been drilled and tapped for sights until just recently when Ilion switched to scope rails only, could be it's an SB1 which comes with the new style checkered synthetic stock and is a slick barrel except for the scope rail, the right side of the frame will tell you if it's an SB1 with the warning they put on it. Lots of possibilities for either SB1 or SB2. Gardner used to install sights for $47(drill and tap plus the sights), dunno what Ilion charges now, but I bet it considerably more, gunsmiths commonly charge about $20 a hole for drilling and tapping, plus the cost of the sights. The Williams WGRS-H&R will work in the two rear scope mounting hole, then you only need a front sight, see Peep and Firesights in the FAQs.
Tim