If you make a tool using a wire clothes hanger, one for each side. 
cut a length about 4 inches (104 mm) bend it so that you can insert  into both holes on one side and when inserted you can pull the radio 
forward, it may take some manipulation but inside the two holes are spring catches that clip into the side mounting. no force is required but it can sometimes be tricky.
                
 Des Long
                
 June 2005