Factory kickdown parts have grown scarce and costly. See
this thread for kickdown options. What kind of car (year/model) is your son driving? If it's a pre-'67 car with the rotating-rod throttle linkage (or heck, even if not) you might want to look at the
parallel 2bbl setup article as an alternative. Photo documentation of a very well done such conversion is
here.
Air cleaner also depends on what kind of car he's working on. If it's a '60-'62 model or it has A/C, that makes it harder to find an air cleaner that'll clear everything. If not, that makes it easy (can just use a 2bbl V8 air cleaner).
