all vectra B 2.2's had the old type oil chain kit fitted at the factory.
if they are going to break they normally break around 41k
the fact that it has 78k on the clock means that with regular (5k mileage) oil + filter changes it should be good until 100k
100k is the lifetime of the chain kit and any 2.2 with that mileage should have the chain kit replaced, cost is around £350 fitted - so compares well with a cambelt change, but will last 100k instead of 40k
personally I would just listen to the cold start up, if there's a rattle it will need replacement asap.