Welcome aboard, woodhick. It's basically all been said, but you did well for little. I like the profile of that improvised barrel, and I also happen to like the carriage; I believe it's made out of mahogany, and well made at that (Zulu, aren't the front and rear transoms attached to the cheeks with dado joints?). I'd go along wth DD's opinion and make larger wheels (the front wheels a little larger than the rear), and I'd also make the cutout in the front transom under the barrel a little larger. Then all you'd need is capsquares to hold the barrel down, and also as DD said you need a quoin (wooden wedge with a handle) that rides forward and backward in the groove cut in the stool bed. If you lightly sand that mahogany, apply a stain (red mahogany, or whatever you like), then a clear finish coat, I think that carriage would look fine.