m4ttyrs

I had an mls head gasket fitted along with a few other things to my escos a while back. now the guy did say to me if the block face wasnt perfectly smooth i would have problems but ford usually do a good enough job from the factory. Now on full boost im having issues with water coming out of the header tank so it seems that the block wasnt perfectly smooth. now what i want to know is, how big of a job is it to machine the block? full strip down? and is this the only way round it? Thanks. Matt