Shackle flip and rear pinion angles

[1986c10]

Hi, i picked up a 95 chevy ecsb a few months ago. id like to lift it and have been reading up alot about rear shackle flips and id like to try it out. In my thinking though, if a shackle flip were done to the rear spring mount, it would drop only the rear of the springs and the front mount would stay in the same location. Wouldnt this drop to only the rear mount change the pinion angle of the rear end drastically? Or am i over thinking it? Thanks in advance.