I have done the modification and all parts were available from ACA.
Be advised it requires some major modifications. I made the change because I had the spring gear and none of the oleo gear. The price of the oleo gear was much higher than the cost of the required parts.
In retrospect if I had the oleo gear I would not make the change. If spring gear was required I would sell the early Citabria and buy a 1975 or later. The late 60,s and early 70,s are a bit strange with the early cowls and 1974 is a one year only type.
Paul
