Since I need the car to run, I have decided to button it all up and make a note for a chain replacement in the future - probably when I decide to replace the deteriorating wiring harness.

After tightening up the 3 exaust cam bolts (which were loose - a dangerous oversight that is now thankfully corrected) and doing a final cheap oil flush & filter change to rid myself of the remaining chocolate mouse in the engine from the head gasket failure, I have filled up with Mobil 1 synthetic 10-30 and everything now sounds quiet and smooth.

Just need to fix a cracked headlamp housing and attach the freshly painted bumper and I'm back on the road.

Thanks again to everyone who replied.