I notice that no one has been able to advise you, it's been nearly 50 years since I ran an ED Racer, so I can't remember thread sizes etc, but I do remember that the ball and socket coupling just unscrewed from the crankshaft. Once that's off you'll probably have to get a modern coupling and re thread one end to go on the engine. I always found Prestwich models very helpful, try contacting them, they specialize in ic models.