Re:
The Chainguide is an AC or "Adventure Components" guide. This was one of the first really good chainguides for downhilling. If you were a racer in southern california in the mid to late nineties, you probably had one of these. This is the top only model, they also have with with a roller on the bottom additionally to further lock the chain on.
This might actually be the first chain "guide", at the time all that was available was chain tensioners like the Mr. Crud roller that attached to the middle of the chain stay or the Bullet Bros. Rear axel arm and tension spring attached to the bottom of the deraileur cage.
I had one of these on my 1994 Parkpre pro 825 that I raced junior 12-14 downhill at snow summit and other spots in socal. This guide worked really well and didn't cause a lot of friction.