Neway do a small engine kit which is fairly standard kit for most mower shops.
Downside it is not cheap, because they are good.
SO unless you are a workshop take it to another workshop.
I charge $ 20 (AUD) per valve, takes about 5 minutes + clean up.
Bought mine 6 years ago and in reality it is yet to pay for itself.
OTOH you must have one to do side valve valve lash unless you always fit new valves.