I thought I had the same problem with my 67 when I converted to a Muncie from an auto. I bought the hole set-up from the trans to the pivot ball from a guy that had everything in a 67 Camaro. I finally figured out that the motor had to be setting in the frame as if the trans was hooked up and on the cross member. If the motor is sagging down in the rear the z-bar will appear to be too short.