With the exception of the Z/28 sb cars used an 11" clutch.
I assume this is a sb car with correct crossmember and engine mounting brackets. The Z-bar has to be perpendicular to the engine. If it has some angle, that is at least part of the problem. I believe the bracket holes are pre-punched in the frame but I have seen them off by enough to make a difference. Also, the mounting bracket is 67 only, 68-69 is different. 67-68 pedal assembly is not the same as 69, which do you have? Are you certain the release fork is correct? There were several part numbers over the years.
Just some thoughts.