The actual shaft angle is irrelevant. All that is required is equal and opposite angles of the output shaft and the pinion itself.
The one thing that stands out here is your measured pinion angle. The factory pinion angle for standard Hotchkis style rear suspensions (read: leaf springs) from General Motors is 4* up, with a output shaft angle being 4* down... which would nearly match your measured output shaft angle of 4* down.
It looks like you will need to adjust the G-Link to obtain the necessary pinion angle. And yes... it is very much important if you want this thing to live. Furthermore, the more power/torque... the less angle necessary. For high power applications, I try to stay under 2*... and more towards 1* if you get near the critical shaft speed of the drive shaft itself.
This is the most simple example:
MW Operating Angles