I misread your post. I took the 22" as the size of the tanks. You are probably right in your calculations with the size you cited. Tanks usually have a certification tag welded to them. By law, they must have the name of the manufacturer, certification, and capacity. We get scrutinized on this on DOT inspections. But I doubt if you would be scrutinized. And because it is a 53 model, you could claim that you meet 1953 standards.