I know that Lapping was an accepted way or re-conditioning the valves in the past... If there was much pitting or recession, you can end up with a "Seat 1/4" wide... That will only trap carbon and Leak.. I would advise having a good Valve Job done while you are at this..and install Umbrella-style (Ford) Valve seals on the Intakes..(Yea, Yea, I KNOW they "Didn't come with them"..put then ON anyway)..!!!
Is there something that leads you to think the Head Gasket IS leaking..?? Foaming in the radiator, or something..??
Possible, the top Compression rings have been shattered, by use of Ether.... Cast Iron Rings WILL shatter if pre-ignition is encountered...Something to be aware of.. Nodular-Iron Rings are Ductile and will NOT shatter, like Cast... Always check to KNOW what you are getting.. Ron..