'74 Scamp A904 issues

The one that you said looks like a speedometer cable is likely the one for the kickdown/throttle shaft under that e-clip in your second picture.
The larger one for the shift shaft should be National Seal part number 8609 or equivalent. Link below.

1974 PLYMOUTH SCAMP 5.2L 318cid V8 Manual Shaft Seal | RockAuto