If the duco really starts flaking and you need to re-wrap, you might try Aquarian American Vintage heads. They're a little oversized to accommodate vintage shells with slightly larger diameters. I'm not sure if the size difference will allow for wrap over a duco finish, but it might be worth a try. If all else fails, you could always tuck your own calf heads for a guaranteed fit.
But I agree with everyone here--your duco isn't pristine, but it looks pretty good from where I sit. Beautiful find!