There should be a clevis at the carb end and a threaded rose/heim joint with a locknut at the bottom attached to the bellcrank. The factory manual describes how to set the rod length -with a suitable lock pin to hold the bellcrank in place, loosen the locknut and unscrew the rod until it attaches to the throttle linkage so there is no tension on the throttle. Once set, if you shorten the rod a little, it will make the box change up at a higher RPM/road speed a little in each gear.
Update -
Have a look at Todd Millers site -
http://members.tripod.com/austin_america/id72.html Update down the page talks about raising the shift points.
cheers
Kevin