I had the same situation. I am using a \6 z-bar, the arms are in the same position as the small block along the tube in relation to the frame side of the bar and are in the same position in relation to each other. The difference is in the length of the tube with the \6 being longer so its was a siple matter of cutting about an inch off.
I too didn't know there was a different bracket for bell hosuing built after 72 and once I got the correct one the angle was correct.