Why not cut the sheets into smaller sizes like 6x7 and load that into an MF back to cut down on waste as you test the film. Or even 35mm... All you need is a dark bag, load the cut film in the back and close it expose the one frame and repeat. You can do it on your back porch (or inside if you use lighting). Saves a lot of waste.
Secondly, give Ilfsol 3 a try, I've had really good results with old film and Ilfsol 3, I know everyone says HC-110 is the go to anti-fog film but I've developed film from 1947 that had less fog than new film with HC-110 (this was only the case of 3200 speed film in HC-110).
Anyway just my thoughts. Also as I understand it and in my humble experience the rule is 1 stop per 10 years or so, assuming your film is at least 20 years old, rating at 100 would still be fine.
Again just an estimation. Try EI 160 as a new testing mark.
Mamiya: 7 II, RZ67 Pro II / Canon: 1V, AE-1, 5DmkII / Kodak: No 1 Pocket Autographic, No 1A Pocket Autographic | Sent w/ iPhone using Tapatalk