Typically a burnt valve might have a small chunk missing/burnt out of the edge of the valve. That could happen even with leaded petrol. With no lead, once valve recession starts there is no flat surface on the valve and head to dissipate the heat and it burns away all round. Gradually both the valve and the seat burn away giving the step shape shown. I've never seen a picture of one that bad. The matching faces will give a sort of seal keep the compression up but a valve with a chunk burnt out of it will not. Besides valves I think you will need new guides. I would get new springs too.
You can get parts a lot quicker if you pay for some sort of express post but that means expensive. Depends on how quick you need something.
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