This sounds like a fairly modified car. So the factory specifications won't mean much. It is much more important to think of the whole drive train as a complete system.
If you have lowered the car the pinion angle changes, change the drive shaft length the angle of the drive shaft changes. All of these angles must work together for a smooth operating power train.
The closer you can get the car to it's finished ride height before setting the engine angle will save you work down the road.
I suggest mocking the engine and transmission in the chassis (at ride height), then using string from the output yoke to the rear end. This will allow you to check that the angles are are in the ballpark.
Here is a link to another site that may help you with your design.
https://www.pro-touring.com/threads/...e+shaft+angles
The Spicer website has some good information on the subject.
https://spicerparts.com/calculators/...gle-calculator
I hope this helps you. Feel free to post any questions.