Two different valve covers means - Use Extreme Caution when evaluating this car!

They surely didn't come that way, so what's the deal? And what else might have been replaced (for what reason)? At the very least it shows that some previous owner didn't have, or refused to spend, the $50-100 it might have cost to get a matching cam cover . . . that tells me he's a corner-cutter. Would a guy like that have changed the oil - ever?

If there are no repair records, I'd only be interested at a VERY low price. In other words, assume the worst: that the engine was bodged and will need to be replaced. What's it worth then? That's what I'd offer (about $5k less than you think it's worth if the engine was original and in good condition).

But I could be wrong.