We recently dug an old M740 (,308) out of my Grand Parents closet. I really don't know anything about these rifles. Can anyone here share some info on them?

They are generally excellent rifles with good accuracy. Much better than the later 7400. I've never had a 740 but I've had several 742's and they all shot MOA or very close.
After thousands of rounds, the locking lugs get funny but in general use you'll never wear one out.