Love these do it yourself/garage builds. Hell of a nice build and some great decisions.
In regards to you driveline angle. If you are using factory driveline angles and it looks like you are,you need to be concerned with your WORKING angles. The DIFFERENCE in your driveline/pinion angle and your driveshaft angle. So, if your driveline angle is 4 degrees DOWN and your driveshaft slopes down 1 degree, your working angle is 4-1=3. If your driveshaft slopes up 1 degree. It's 4+1=5. Your pinion angle is the same concept. When you tallked about the magic 3 degrees, it's working anlges, not the difference between your driveline and pinion angle.