if the carb is setup for an automatic kickdown, then just snap the cable on.
if the carb is from a 4 speed or big block vehicle, then you may be screwed. they don't always have the lower half of the linkage down there.
if the linkage is there, but no stud, go to your local auto parts store and get a kickdown stud from what i call the "cheap chrome" section- you know, that little corner of the store that has maybe a Performer intake, a set of Edelbrock valve covers for a small block, and a bunch of Mr Gasket chrome parts like breathers and throttle cable mounts. sometimes, they will have the Edelbrock kickdown stud for a few bucks.