Rolex no crown guard submariner ref 5508 versus 6536

Information from the forum 

The movement on the 6536/1 is a calibre 1030. The 5508 calibre 1530 which was a more modern and reliable movement than the 1030. Both are so called 'Butterfly movements' because of the rotor which is shaped like a Butterfly on both the 6536/1 and the 5508 (see picture below). 

Movement Left Rolex 5508 and Right 6536/1 

The outer case back of both references are quite different. The 6536/1 is on the right and is quite different in shape than the smaller diameter case of the 5508 on the left (see picture below). The inner case back ofcourse is marked with the respective dates. On the left you have 5508 which has the smaller diameter also on the inside of the case back. It is also clearly marked with the date 1958. On the right you have the date marked III 1957 - third quarter 1957 of the 6536/1. See picture below.