My Bear Super Grizzly went unstrung for many years. It was always stored in a house, never in a garage or attic. Ask your friend where it has been stored. If in a hot attic, be careful. If in a garage, also be careful unless the garage was climate controlled.
Even so, if you've checked it over and are confident it is in good shape you might as well string it up if you intend to shoot it.
I check mine for twist by placing it tip up and on a flat surface like a kitchen counter. If it sits perfectly flat with no wobble then you're good. If it wobbles and you're certain the counter is flat, then you have twist. Putting the string on reversed helps too. With bow relaxed take the string and loop one end over the a tip. Take the string straight to the other tip across the face or front of the bow and loop it over the other tip. Now sight down the string looking for any visual twist. The string is usually just short enough to put slight tension on the limbs this way. This is how I store my Bear.
Congrats on the gift. Sounds like you're gonna have a fun future shooting it. Those old Bears are tough.