I added another "driveshaft" line to the picture to show what happens if the angle at the diff flange is 5 degrees instead of 0 degrees. The result is a difference in height between the diff flange and the t-case flange of 18.8 inches @ 5 degrees vs. 15.4 inches @ 0 degrees. Basically, unless you're flanges are 15.4 inches (vertical) apart you don't have a 0 degree angle at the diff flange.
You can't draw the entire picture unless you have measurements for two of the three triangle lengths. Having the angle of the driveshaft, like Jesse suggested, would also work.
Make more sense now?
bd
I'll be using string to get the shaft angle here in about 2 hours.
You walking to work these days?
Just these couple days.