well at least it hasn't cost an arm and a leg like it could have done if the head was warped/block cracked. just a headset.

Is your sump not provided with an outlet for the breather? as that hole at the back of the block may well be under full oil pressure if it's the one I think it is. The breather on a zetec block is usually on the front but if fitting a turbo, needs to be blocked with a core plug or blanking plate and relocated normally to the sump, or mine is.