I have a 350SL 1975 euro model. It has a 4-speed manual and a V8 of some kind, alloy block. The original motor is cast-iron 3.5 and in my garage. <br> <br> They are similar. As I think, the 3.5 / 3.8 / 4.2 V8's are all M116 motors. Correct? So how can I tell wether the motor is a 3.8 or a 4.2?