The injected engine blocks are wider in the front chain gallery area. As a result the fuel injected heads are wider in the chain gallery area. Note there is a chain sprocket missing in the chain gallery of the head of the carbureted engine since there is no room for it. Also with the injected heads the valve cover surface on the manifold side is serpentine-like (curves). It is straight with carbureted heads. Earlier MB injected engines (220SE) with injectors mounted in the intake manifold did have a straight valve cover on both sides, but the heads were still wider at the chain gallery since their blocks were also wider in the front to accommodate the distributor and fuel injection pump. A carbureted head will not work on a W113 engine.