Super, with a lead replacement additive from www.millersoils.co.uk Ideally, the engine needs to be stripped down and the iron exhaust valve inserts replaced with harder chrome steel ones. But this is a big job. Thinking about it, if this engine has been laid up since 1984, it needs to be completely rebuilt because its part alloy and part iron construction will have led to internal electrolytic corrosion and the cooling system will be blocked up with sludge that accumulates at the back of the block, leading to localised overheating there.