After a long wait, I finally rebuilt my engine and replaced the clutch with a RAM type. Now the ZBAR is bending and I can't figure it out. (67 Fastback, 289, 3 Speed, in storage since 1973)
I ran into a similar problem, and I was partly the cause. The orginal Ford z-bars were made of high quality steel, that could stand the stress. If you have re-bent your z-bar to clear headers, etc., then you may have weakened it. Especially if you heated it.
If you are using a repro z-bar, it is just not strong enough. I did both things, and the final solution was to reinforce the z-bar by welding additional 1/8" plate steel to it.
Man a 67 Fastback in storage since 73, Thats sweet. A friend of mine had the same problem in his 68 he did as the first poster did, he took car and all to weld shop so welder could weld braces for clearance, it works good. Good Luck Dave...