I made one years ago by studying how the stock parts worked. You have to refile the 2nd and 3rd (former 1st) detents on the shift plate. As I remember I filed them upward (this was over 25 years ago). Then I fabbed the little spring loaded part that stops the the handle detent. It stops the detent in the handle and then pulls it upward. I know this is not a complete instruction. I built this when I first started hot rod stuff. I was young and had no money. It worded very well and didn't take long to figure out.
Doug