What brand? I'm assuming you are talking about putting the tracks from a 800 on a 900.... Anti-rotation brackets are very likely different, sprockets may be as well (different engine / different gearing, at least with Camoplast / Tatou...)
Well that really depends on what kind of deal you can get on the used set of tracks that you know of. The ones I bought were practically new and picked them up for $2200. After the transfer kit, I'm into them about $2900 plus my time. A lot better than the nearly $5k for a brand new set.thanks for sharing your wisdom sounds like i would just be better off getting the right ones fit for the machine