Having 9 degrees of pinion angle is kinda scary, regardless if it's positive or negative. Spicer's web site used to recommend a maximum of only 3.5* U-joint operating angle (aka "pinion angle") with their U-joints.
-9.00 degrees of pinion angle (driveshaft C/L vs pinion C/L combined to form U-joint operating angle) on a ladder bar car makes for a whole lot of possible U-joint binding going on under launch loading. And if that rear 9* pinion/operating angle is way off what the the operating angle up at the front slip yoke U-joint is, you can end up with a decent front/rear U-joint phasing/vibration problem.
With a ladder bar car I usually use a range anywhere from -1.00* to -2.50* pinion angle/U-joint operating angle between the driveshaft C/L & the pinion C/L. The "best" number to use really depends on how much power the car has to work with, if it's a "strip only" car vs a street/highway driven car, and what the U-joint angle is up at the front slip yoke. On some of the top of the line "Pro Mod" style 4-link setups that use fairly large diameter tubing (for the 4-link bars) I have seen as little as -.75* (three quarters of 1 degree) to -1.00* pinion angle because the large diameter bars flex/bow so much less than the 4-links with smaller OD bars.