There has been a recent upsurge in special
oil for flat tappet engines filling a niche we all have been complaining about. Like Keith said buy the darn
oil and be done with it. You don't need to add anything. Here are some you can search. JOE GIBBS HOTROD
Oil,
AMSOIL Z-Rod oil, BRAD PENN Grade1, LUCAS HOTROD & CLASSIC. There all out there now. Viscosity will depend on your clearances.