Been there done that!
I have the same year and model. I changed out both the throttle and shift cables a few years back. It's not that difficult, but somewhat time consuming. You have to remove the compass from the pedestal, and essentially, snake the new cable through the pedestal to the engine. ONE BIG THING TO BE CAREFUL OF! Make sure you measure the length for your new cable wisely. Too short, and it won't reach, too long and the cable will bind and you'll lose some control. I know because mine was a about a foot too long. It took a while trying to figure out why the new cable wasn't shifting properly, until I had the Admiral shift from the cockpit while I observed what was happening down below. Also, remember to use care in loosening and tighten the clamp screws... they probably haven't been touched in 35 years!