Other issue worth mentioning is you are still probably better off going for an earlier cam belt kit with the adjustable lower pulley rather than the correct one for your car as it stands now.reason being if you do end up skimming heads then a non adjustable pulley may leave you with valve timing slightly out and no way to get it right on that bank.
In that case the cheapest way to get a kit, with an adjustable bottom guide roller, is apparently to buy two of the below kit. Remove the required roller from the surplus backplate and if necessary reuse the washer currently on the engine. That also gives you a spare belt in case you disturb the cams again. Total outlay £39.98. Possibility of 5% off as well.
If the tensioner/roller backplate in the kit doesn't fit your engine then it's fine to swap the upper roller and the tensioner roller from the kit onto your existing backplate.
Other members on here have previously reported doing this. The bearings are the same SKF ones used in other kits. AC Delco is GM's own brand so the quality of the belt is going to be at least as good as any of the others.
AC Delco Timing belt kit Vauxhall Vectra Calibra Cavalier 2.5 Omega 2.5 2.6 3.0 @£19.99 ea delivered.