Ok, I did wonder about that, but wasn't going to open the door.. as backpacker has: Hypothetically it should be perfectly possible to complete a loop with mild and entirely positive G, within the certified G limits of the aeroplane. It won't be round, but...
Barrel roll is probably one of the nastier ones if done as a proper barrel roll (rolling G), let's not start the 'is a one G manouver' misconception. What a lot of people call a barrel roll is really an aileron roll and not half as bad..
As has been said, there's no reason the wings would fall off, but there's very little margin for error, and very good reason to do so.
The aforementioned whip stall sounds a lot like a tailslide, or at least something that could very easily turn into a tailslide - in which case the biggest likelyhood of damage through mishandling is to the tailfeathers. As anecdotally they seem to flap around a bit on the '38 (never flown one), that would seem a good reason to avoid.
Quite simply there are plenty of perfectly good aerobatic aircraft out there designed to take the stresses, and also to leave you a reasonable chance of getting away with minor stuffups. Why risk it?