Agfa BW film expired in 1974; any sugestions how to shoot/process it?

A friend of mine bought a bunch of vintage photographic equipment from
estate sale.
In one of the bags, that he got with it we found this 120 BW film.
It is Agfa Isopan ISS, asa 100; stil in original packaging- looks quite
fresh ; )) I mean the box hasn't even faded and is bright orange. Its
expiration date is Jan '74 : D
I'd like to do some portraiture shots on it.
So, I guess it has lost it's speed, probably a few stops. I'm thinking I
should probably expose it at EI 25 at least, maybe even 15. Than... I guess
I'll put it through Rodinal(?) Not sure what dillusion.
Any suggestions on how to deal with this geriatric emulsion ?!?

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