Buy a new tach cable and lube it with tranny fluid before install. I hate to say it, but make sure you buy new gaskets for the tach, instrument cluster and Speedo. if the speedo bounces, send it out to Speedometer.com for fixin. worth it. And you may want to put in LED bulbs across in all the gauges to see them at night, the old 2v incadescents suck. make sure you have a retractable magnet so you can retrieve the dropped parts. Keep Band aids nearby. You really don't want to do this procedure more than once in your life. And we haven't even mentioned the heater control levers yet. Ooh, bad memories. I have the luckiest zip code in the world as I live 4 miles from Joe Alexander.
Oh Yeah, the $30 per year SL113.org membership for technical access is the best money you will ever spend. Good Luck.