the oil gallery is underneath the exhaust monifold quite difficult to see even on a ramp due to fittings ect. had a look on auto data they say 12hrs to do cam chain but did not give how to, can't remember if the head has to come off to replace chains does the haines manual give a clue
I did the cam chain & sprockets on my CiH 2.2 Carlton with the head in place - 4 pot version of the 3.0 12 valve straight 6.
I think the head can stay put, but bighead has an oil leak he wants to sort.
At 84k miles I doubt your chains will
need replacing, but more likely that the 'rubber' chain tensioners will need replacing, James W in the ABS I think is the man you want, as IIRC they are NLS (No Longer Stocked) at Vauxhall.
...... but of course it's up to you. It'll cost you a couple of hundred to do just the CHG by the time you've replaced manifold gaskets, head bolts, etc etc