that's a great guess. it looks like there was a lot of xc pro Suntour on the stumpjumpers in 1991. i am sure the suntour group is OE and the x-1 is many rungs down the ladder from xc pro but it will really help to figure out when this bike was mass produced. 1991 sounds good to me. OE was mostly shimano with a smattering of Suntour