A colleague recommended a machine shop / engine specialist in Coventry. I've purchased 8x exhaust valves and will have the seats and valves worked together. Might as well have it done properly.

I'll ask them to check for warping and replace guides and seals same time if necessary.

The head will definitely flow better if all the seats get a multi-angle re-face.

So unfortunately it turns out the head was cracked when pressure tested. Waiting to collect on Friday and to see what / how it could have cracked... I'm told due to the location it's not repairable.

Can anyone recommend a good place to buy a vvc engine or head? There are a few on ebay around the £500 mark at the moment, but are there any more trusted locations to pick one up?

Care is required when buying used K series heads. I recall an article (might have been on DVA website) that said that many of the original castings weren't that great and also many weren't properly peened/hardened on the face, hence why even a small skim can expose soft metal and lead to further problems. I'd say you are better buying a whole engine than just a head as bottom end issues are less common than head issues so in theory there shouldn't be good spare heads floating around!