Don't know if the Beaver has a fatigue limit on any airframe parts - the Twin Otter certainly has a life limit on the wing, which can be replaced (and has been in the past) to give the aircraft a new lease of life.
Assuming that one has the aircraft log book and therefore knows the total time, you can then make a start. Certainly a thorough inspection, plus replacement of seals in the fuel system, would be a bare minimum, plus engine work, dependent on how long it had been out of service. There aren't a huge number of electrical components, and I would guess they are mostly 'on condition' anyway.
Having said all of this, the market for DHC2's was such that anything remotely resembling a flyer has already been hoovered up, because a good 'un was worth $250,000 not so long back. A lot of old ships were able to head airborne again, simply because of the economics. What's left inactive now is mostly in the hands of museums who would not let them go.
Makes one wonder where all of those ones the US Army retired ended up - there were rows of them at Davis Monthan once....!