You need a 3 bolt type puller to remove these balancers properly.The 3 jawed type puller can stuff the balancer as the balancer is made from two pieces of metal joined by rubber,and if the balancer is pulled off the engine from around its outside ,the inner metal part of the balancer can seperate from the rubber part which will render the balancer unusable...These balancers arent cheap to replace either.($300)
With the 3 bolt type puller,you will need three 1/4 UNF bolts about 2 inches long.These bolts screw into the slots around the balancer so it can be pulled off with the puller.I got my 3 bolt type puller from supercheap,it only cost around $20,it came with some bolts,but none had the 1/4 UNF type thread I needed for the commodore balancer,so I went to a hardware store and bought the right bolts for a couple of bucks..Ive used it heaps of times,and it works excellent every time,Ive even used it on engines that have been out in the weather for a couple of years and the balancer has still come straight off no worries..To stop the engine turning,get an old serpentine belt and wrap it around the balancer and then twist it up really tight with a steel bar so it cant slip,and get someone to hold it,this should be enough to stop the engine from turning whilst you remove the balancer,or as already mentioned,you can remove the starter motor and jamb the engine up with a screwdriver locked into the flex plate..
