Don't know what year yours is, but have found a few with also a idler pulley, unless my old age is fooling me and that was the mk2 astra I had!!
If doing a stat I would do a water pump at same time, cheap enough around £15, and stops all the hassle if it goes and starts leaking 5 minutes after doing the belt.
I always do a nerw stat and pump at same time as timing belt, ie every 3 years.
tabetha