I don't know if ford used sodium filled valves on on any of the FE engines other than the "Cammer" and they are obveosly a much larger valve than used in the 427 wedge, if you have means to size them up you'll know if their sodium filled.
I don't know if there are markings on them for ID purposes
Only the exhaust valves were sodium filled. They are a sodium/mercury mix and you don't want to use them! They can explode with any contact to water or to air if they break open. Very dangerous. Back in the day they were great but not so much today. You can look for a darkish discoloration at the base of the stem. New/NOS or used not something you want around. The intakes on the other hand were hollow and fine to use if in good shape. You want to dispose of the sodium filled valve at the nearest HASMAT transfer station. Explain to them exactly what they are and to handle with great care. Exposure to the sodium/mercury mix can make you very ill if exposed to it. Sorry to sounds so grim but it's the honest truth.