Upholstery Bob? Sounds like your getting real close to taking her out for a joy ride. The barrel clips just hold the vinyl cover to the outer frame rail, which is flat-formed steel. The padding is hog ringed onto the inner wire frame with standard hog rings. Take a look at these pictures; they should answer your questions.
http://www.pbase.com/dennygraham/ad_interior&page=4 My cover from JC didn't really fit all that good and there were wrinkles that I couldn't get out. Next time I'll do it myself or have it done at an upholstery shop.
The original cushion was burlap-cior (horse hair)- single layer of cotton and then the cover. The back was just burlap and cotton. I stayed with the original padding stack configuration and the seat is surprisingly comfortable. My wife and I have traveled close to 8,000 miles in her, sometimes a couple hundred miles at a time and we don't have any complaints about the comfort.
Denny Graham
Sandwich, IL