I have no recommendation on exposure. I would tend to expose it at the rated speed (e.g. ISO 400). HOWEVER, film that is stored for a very long time accumulates radiation due to cosmic rays...even if stored in a freezer all that time, and even if stored under ground all that time!!!
There is no escaping cosmic rays, they go THRU the earth. and they fog film with accumulated exposure to cosmic rays.
The film speed may not have changed, it simply has an overall fog even if totally unexposed to light for all that time. And color film may exhibit color shifts so that it no longer portrays colors with a reasonable degree of accuracy.
I'll leave it to those with considerable experience to using old outdated film to make recommendations.
Rumored to have been offered at a grocery store chain, A&P, and named for the company president.
Rumored to be Fuji made