Okay, Mike. If you are going to drop the trans pan anyway, to get to the shift body, where the piston (or valve, as it's also called)...of course, you'll be draining the fluid. Be sure to look for any trash in the fluid!!! Will call for a new filter, gasket, fluid, lol.
With a service book in hand, you'll see the break-down of the shift body, and which valve is the kickdown. (It's ALSO for throttle pressure. You might as well understand that.)
The shift body can be removed, or replaced, bottom line all valves need to move freely.
If the kickdown is hanging for whatever reason, needs to be fixed, or the entire shift body replaced. Fixed by completely busting the shift body down, and cleaning it. If any scoring, or the like...it's junk.
The Edelbrock carb...could need an added piece of link 'arm', to get correct swing at the throttle shaft. In the car's service manual, set-up for kickdown linkage/rod. If you have some Mickey Mouse set-up, toss it over your shoulder, and get something that works.