Is that the transmission kick-down you are referring to? Is it cable-actuated off of the throttle cable on these?if you look earlier in this post i put a couple pix of the engine on here. i bought the throttle mount on Amazon.
Stain Aluminum Throttle Cable Bracket for 4150 Style Series Carburetor
then you need to mod something to link the throttle cable to the carb to the kick down.