Looks like this piece was used on:
cb400f, cb500, cb550, cb750. The 900 is a dohc and doesn't have much in common with our bikes.
A good way to find this stuff out is to use a site like this:
http://www.babbittsonline.com/pages/parts/viewbybrand/7/Honda.aspxLook up the part number first (on the left) and then type it into the part number search (on the right). It will tell you the years and models that used the part.
There's a few on ebay for around $20 or $30, which seems a little high. Maybe you should list it in the parts wanted section on this site.