Bore was cleaned up with a flap wheel as suggested, followed by a sanding pad with plenty of maintenance spray.
When I cleaned up the head the lack of head gasket was revealed... there isn't one, this seal sits in the recess in the head. But I only found out after I had damaged it with the wire wheel.
Not sure what's going on with spark plug, this is the one that was fitted (which looks like one for a Ford Pinto engine) but the hole isn't fully threaded anyway.
Piston cleaned up.