Hmmm...
Holy cam-carriers!
It's not a minor job then H? When you said you had overheating problems I had visions of a new thermostat or something.
Appropos of not much, my Grandad used to be a Jag dealer in the 1950's and early 60's. He ran many an S type and Mark II, including the fabled 3.8 and knew them inside out. He loved the cars, but was never too keen working on the engines. But from what I can remember, he always reckoned keeping the cooling system in pristine condition was of paramount importance, insisting on regular flushing with radiator cleaner and running the correct antifreeze mixture to prevent corrosion and deposit build up. Absolutely spot-on valve and ignition timing to prevent pre-ignition were his mantra too. Not easy when the product of Joe Lucas enter the equation.
I'd ask him for his advice, but unfortunately he's dead now, bless him. As far as I know, he never messed with Anusol, but he was a stickler for Fybogel (The Bowel Regulator) and Fiery Jack.