Pinion angle question

The general rule of thumb is 5* pinion nose up from the spring perches. Here's how I do it. Get some concrete blocks and stack them right there the perches will be. Make sure the blocks are level front to back and side to side. Place the perches on the blocks the same width it will be in the car. What is it? 43"? Now, measure to get the rear end the same distance front the backing plates to the perches on both sides. Finally, position the rear end 5* nose up with the pinion center line. Weld away. You want nose UP just considering the rear axle by itself, even though it will end up nose DOWN in relation to the transmission.