So I got and dismantled a camping stove. Now I have a variable propane regulator and a decent burner! Unfortunately, it's only about 16 inches long, so it needs a smaller case. I'll look for a small metal drum.
Now I have a good idea for spinning the spit! Imagine two rubber wheels on each end, outside of the oven itself, spinning slowly in the same direction. The wooden spit can rest on top of them and spin at a similar rate. This way I don't have to worry about hooking gears into the spit itself; all the chains and necessary things are attached to the wheel rig. However, I'd have to make two wheel rigs, one for the oven and one for applying batter.