Anyone swap a Tremec T45 in their 67-69 Dart?

No its an add on gear box that I think is controlled by switches. If you want to bang gears you'll need a manual trans.

https://gearvendors.com/index.html
Anything short of stock 4 speed will require a larger tunnel unless you go with American Powertrain and even then there is surgery. Stock will still need the hump installed.
Yes, I am aware of the fab work involved. I am going to go with the 3 speed OD, manual.