I believe that Maury intended to use high-pressure sawmill type engines and boilers for his gunboat class. They would be high-output systems, but also high fuel consumption. The engines and boilers wouldn't have been a big problem. A stumbling block would have been the gearing and the propellers. Side-wheelers tended to rotate about 20 rpm. Screw machinery ran about double, so the gearing was necessary. The draft on these boats was more than you'd expect. Contemporary British gunboats of similar displacement had drafts of 4-6 feet. But the deeper draft of the Maury boat would have provided greater stability when firing both guns at a target located parallel to the gunboat. The British shallow drafts were very marginal in action in terms of stability when engaging with both guns in broadside orientation. There was a pronounced roll. This is also the reason that the British light drafts had 4 foot bulkheads.