The mini-tach is no longer manufactured. You can adapt a Jeep CJ tach to the hole. There is also a conversion tach, full-size, that installs as did the factory tach, but adapted for the standard cluster. Apparently, a competitor is about to introduce a similar full-size unit, giving us two sources for the conversion. Using one in a 68 would require adding a 67 "GASOLINE" gauge, as well.
Jeep CJ tach installed-works great!