What's in the ad is minimal info. There are a series of ADs on those airplanes, including an annual check for rot at the wing roots and spar attachments, a tap test all along the spar itself to look for delamination, landing gear bracketry at the spars (they crack), engine mount cracking, horizontal stabilizer spar attach point in the fuselage cracking, and so on. Removing the fabric typically exposes more defects that need addressing, too. I did a bunch of work on a Viking not so long ago, and found a whole lot of stuff that had been left by other mechanics, including loose flap and aileron hinge and bellcrank attachments in the wooden control surface spars, and the wing root fairings had been glued on so that the AD inspection of the spars had been impossible. Flap up-stop blocks were missing.
The left wing had its inboard rib bay packed full of mouse nests. Took me hours to get it all out, since access was poor. Filled a garbage can with the stuff. Long-dead mice mixed up in it.
Old airplanaes are fun. Expensive fun. No such thing as a cheap old airplane.