Welcome to the forum, DenverDuck. First: For 200 bucks, that's a good deal; on electric auctions people pay over a hundred dollars for just those size wheels alone.
Second: I enlarged your pic of the muzzle of your cannon, and the tube appears to be cast iron, and I can't detect a steel liner. Take some sand paper, and remove the paint around the bore on the muzzle face; if it has a liner you'll be able to see the ring where the steel meets the iron. This is my personal opinion; if the tube doesn't have a seamless steel liner of the proper wall thickness, then I would never fire the gun. Find someone that that knows what they're doing, and have them make, and install a proper liner for your gun. I think one of our sponsors (Dom Carpenter) has done this for other members.