I would get myself some cotton buds and methanol or model fuel. Just keep rubbing those seats until they are nice and shiny again.
Regarding the exhaust valve, you can scrap the stem with a piece of sharp plastic, like a APC prop, to remove the carbon, but never with a knife, as the stem needs to have a good workign surface on the valve bushings.
For the valve face, I would sit it on the head, with springs and collets assembled to keep it closed, and give it a pass with the wire brush of a dremel, as suggested.

Assemble everything up and check for hissing when pulling on the compression stroke to see if there is a need for valve seating with the rubbing compound. Of course, put a few drops of oil on the parts first or model fuel.