If it is the same as the 16 valve then yes you can secure the pulley using 2 bolts to the backing plate, if I remember correctly the threaded holes are at about 2 o clock and 10 o clock positions.
I used 2 bolts from the cam cover.
When you refit the pump dont over tighten the nut as the pulley can crack.
There are a few 'how to' videos on you tube on astra's and vectra's. they have the same engine