I put a 1984 Lockup 904 into my 65 dart, but the shift linkage solution is the same as your 66.
Here's a link to my thread. The very last post covers the shifter cable solution I came up with. I used a B&M cable. Since the post I've put about 500 miles on the car. So far it's worked flawlessly.
A998 w/ Lockup in a 65 Dart with 273