I suppose if you searched Google (not here, the search feature here isn't very good) for CB450K3 (or K4) head rebuild with Honda Twins added to the end of the search sentence, you might find one. It's really not difficult, check the valve guides for valve fit, the valves for dished sealing surface, the seats for any excess wear, cracks or damage (if it was running okay before, not all of that is very likely), replace the valve stem seals, inspect the followers and cam lobes, and inspect the cam chain guides for sprocket wear and sloppiness. There are 2 different pairs of torsion bars, marked A and B - they go on opposite corners of the head, don't interchange them