GAF 120, ISO 125, Expired 1973

I have no idea how this film was stored throughout its life, but I'm itching to shoot it in my YashicaMat.

I will be sending it off to oldschoolphotolab. Should I expose it as 125, 100, 80, 50? Any special instructions I should send to the lab? I've sent them plenty of expired color 135 with usually good results, but nothing this old.

Thanks

I usually subtract 1 stop for every 10 years of expiration, especially when I don't know the storage conditions. I shoot a lot of expired film (some as old as the 1940's), and this formula has worked well for me. If I'm really doubtful, and don't want to lose a shot, I'll bracket as well.