68 Cuda P/S converting to 73 K-Member with Manual steering

Im converting my 68 Cuda with P/S to a 73 K-Member with Manual steering LBP & disk brakes.
Everything is there from the K member to the steering column except for the steering coupler .
I understand that my old one will not work , I here that its to long and incorrect shaft size .
Where can I find one ?

Thanks
Donnie