I just did one on the 600, not a lot of room. Somewhat easier to get the old one out (Which was cracked) vs. the new one in. Removed the steering post, the rubber boot between the throttle bodies and the air intake, and then ended up removing the side panels (Upper and Lower) to give just enough room to work with getting everything back in (And it was still tight). Might be different on the 858 though. Good luck with it, just take your time and keep everything organized! Country Cat does have an online service manual I was referencing for the 600 which helped on some things.