Kickdown and shift linkage questions/pics

The TP rod stays actuated by the carb linkage as normal.
All you are doing is making a cable move your shift linkage arm on the trans.
Tunnel mounting position is wherever is comfortable for you that it doesn't contact the dash or seat.

I routed my cable to follow the floor pan up under where the headers meet the block and then looped back down to the trans using as little flexing of the cable as possible.
Then I tied it to the starter to keep it off the headers.