Jim,
You are probably not going to like my answer, I have the same exact setup on my 69 GTS. After I installed the headers with the engine and trans in the car, I tried to install the z-bar. The z-bar hit the bottom of the fourth pipe back when the clucth was appiled half way through its travel.
I called TTI and asked the guy about it. He said they have been making those pipes for over 10 years and NEVER had anybody complain about not fitting. Basically TTI had no symphathy for my problem. I could have sent the pipes back but they had scratches from installing them, so TTI was going to hassle me about that.. So I started to bend things.
Long story short, I bent the header pipe in for clearance and cut and welded the Z-bar so that the lever was further away from the pipe.
If you need any more detail or pictures you can PM me.
Or if you have better luck by some other means please let me know so other people can avoid the same problem.
Kim.