I recently replaced my missing vane type antenna with a batwing. I purchased the entire package, but ended up only using the batwing, and one of the coax cables and the electric antenna amplifier.
The crank-up mechanism was identical. The batwing mounted on the original risers like it was made for it.
I am thinking you might be able to get the parts you need from the manufacturer of the batwing. The name slipped my mind right now. Do a search, I am sure you will find it quickly. I am going to replace the rest of the antenna once I need other repairs on the roof, like replacing the aging AC shroud etc.