Well consider this: half the studies/grades involved in getting an organ diploma are at the piano and away from the organ.
In a conservatory where 10 years or levels are necessary to get a diploma in piano or organ the first 5 years of organ classes are identical to the first 5 years of piano classes.
The difference then will be in action and mechanics of playing, facing smaller keys and less octaves in the keyboard, facing an additional keyboard, pedals, third staff and learning registers ... and of course building repertory.
Although the action is different the coordinative foundation regarding fingers, hand, wrist, arm, contradition, relaxation, loose joints, hips motions at the piano applies to the organ as well.