Have done a headgasket on a 205 block, and most recently done another as part of an engine rebuild.

Didn't notice any 'lines'. It's hard to determine what you mean by 'line'. Is it a physical groove, or just a mark/discolouration?

It's a bit late now, but ideally you could have re-surfaced the block (known as 'decking') which would hopefully clear up any 'lines'.

Or, a crack test, or at least get it inspected by someone who knows what to look for.

I really hope that it was nothing more than a bit of deopsited carbon and that your car runs like a dream. Cossies can test patience