Can I use the stock kickdown switch on a 66 442 that originally had a Jetaway if I am now using a T400 or do I need to use a later model kickdown (like a 67)?

 

You can use the one you have! Just connect the yellow wire to the terminal at the transmission and leave the yellow/black one disconnected...
You can measure it, too, as you have to have 12V at the transmission at WOT!

 

X2 - using what ya got.

 

I found a kickdown switch from B&M you can bolt to your carb mount or manifold. It's adjustable so you can Jetaway from a trigger point before wide open. I set mine to launch as soon as the secondarys crack open. Wheeee!!