The prototypes of the Mirage IIIR had a particular look. They had the nose and the longer front fuselage of the definitive Mirage IIIR but used the Atar 9B of the Mirage IIIC/IIIB. Here is the 2nd prototype at 2 different times in its life.

Build thread is here (in french, check page 2 for pics of a IIIB build). Design thread is here (in french too).