I know this doesn't pertain to Cubs but since several of us have other tractors, I thought I would share this, picked up from another forum.
Napa sells a universal spedo cable [part no 615-1795] that can be used to replace many different tach cables. Simply cut to the proper length, crimp on square drive end and you're ready to go. This is the cable only, not the shield. Just made 2 for my 560&660 work fine.