they are not suppose to fail at all, the issue was with the vectra b's 🙂
reasons why they fail is most likely due to lack of oil as a result of many things , i.e your burning it off or your leaking it out
be interested to see how many of these astra 2.2's fail and what oil they were using at the time
common fault on astra 2.2's is the rods creating a nice hole in the block, but whether it is down to the owners revving the tits off em , or they using very thin oil or lack of oil
back to your 2nd hand engine then it might well be worth changing the chain as u dont know how long it has been sitting there, it is like any other 2nd hand engine, it is easier to service em when they are not in the car rather than when they go wrong after you dropped them in