I don't think this plane was fiberglassed. Looks like they doped the wood and then painted it. Without Dacron, that finish would crack along joints very easily. And then some of the scars look like crash damage. Wiggle everything and see if anything moves. The plane is likely air worthy.
Snap21's were nasty, ill tempered planes that bit many a pilot early on. But they can be tamed. Limit the elevator travel. Crank up the ailerons slightly to reduce the tip stall tendency, and add nose weight. You can never completely remove the snappy tendency of these planes, but you can improve thier personality with these few changes.