They don't heads or head gaskets for that matter.It is all just one casting of alloy with a steel sleeve for the bore.
See below.
[Linked Image]
Hopefully it will be a decompressor valve or both,as other than that the rings could be be shot.It also is a common problem with them.If that's the case sorry you just won't find any spare parts for them as there is none.
Good luck I hope it's not bad.

Here for a good time,not a long time.