That speedometer cable is for 60-65 and as you have found is unique on the transmission end. A 65 slant/904 uses the same cable; if the car was a 65, then the transmission was either changed to a 66-later or it might have been a 66 Dart. As long as the outer cable is good, just install a new inner cable. $150 is a good starting price for a new cable for that type!
EDIT: If you're using a 65 833, that's the speedo cable you have to use.
