I had to swap the ends of my speedo cable on my 165 to math-up with the 185 transmission. It's very easy, most of the diffculty comes in the form of reaching the cable mounted to the transmission from the top...
With a small pair of channel-locks, follow the cable from the firewall to the top of the trans where you'll fine a ridged collar securing the cable to the trans housing. Loosen that collare, and you should be able to unscrew it and remove it by hand. The other end is clipped to the back of your gauge cluster. Again, the only difficult part is getting at it. Once it's unclipped and unscrewed from both ends, it's simply a matter of pulling it through the rubber grommet in the firewall, and replacing.
Out of curiousity...why are you replacing the cable?