Need help with Speedometer cable

I purchased a 1970 Plymouth Valiant with a 318. The previous owner stated that the tranny installed was from a vehicle with a 360. I need a new speedo cable. It's 63" long. The end that plugs into the transmission does not match the new speedo cable I purchased. The end that I have on the vehicle is a large nut that holds it in. (greater than 1"). Can anyone assist with an application or part number that would steer me in the right direction.
thanks,
Danny