By early flattop grips I'm guessing you are referring to the old model flattops, and not the early new model flattops?
The only old model flattop I've had had factory black plastic/ rubber grips that had the same contour as the others.
The grip frame is smaller, and that may be what you are referring to. They are the XR3 frames. Basically, where your pinky sits when firing the gun is shorter and more forward, similar to the Colt SAAs.