Outdated Kodak 6x6

I got a hold of some Kodak 6x6 films, four rolls. Expiration date is October 1976. and ISO rate is 320. I have no idea what ISO rating to use while shooting nor what should my developing time be. Appreciate the help.

If it is Tri X professional I would be suprised if the film is still good almost 40 years old. My experiance is that slower films hold up better than fast film. My best guess is that I would shoot at 200 and develop with a low fog developer. Good luck.

I'm shooting some 320TXP from 1977 lately. It's very nice rated at 100.