1) he doesn't mind being touched on his head at all (i read elsewhere that this is a bad sign of health?)
I wouldn't read into that as a sure sign he is ailing, and yes many ball pythons are head shy, there are a few here and there that could care less.

2) he has had a small strip 4cm long and 2mm wide along his neck (dorsal side) which looks like it could be a scar.
Without a picture its hard to say. You said its been 2 sheds? It *could* be a burn thats healing, which usually takes a while to clear up (longer than 2 sheds). Just keep an eye on it to make sure it doesn't open up or become infected. These guys can bounce back pretty well with just good old proper care, so just keep an eye on it and be aware of any changes.