Just remember to add 1 degree down to the differential before you weld the perches to the tubes and you'll be fine. With a leaf spring scheme, as power is applied to your rear end, your differential will try to roll clockwise as you look at it from the driver's side, lifting the front of the differential upward. Put another way, your top leaf spring will "wrap up" (deform) allowing this rotation. The extra 1 degree will keep things correct because when wrap-up happens that 1 degree will disappear. Wrap up will be higher when your truck is loaded and lower when it isn't but even with no load at all, it will occur. And also if you're moving your differential backwards, please be mindful of how your springs were designed and don't move it too far back. With leaf springs you have what is known as bias. The front part of the leaf spring assembly generally just locates the differential. The rear part of the spring is what determines your ride quality. Less bias in the rear and you'll ride softer and quieter. A little more rear bias can help with cornering but will stiffen the ride. Too much rear bias and you'll ride very harshly. More bias in the front and you'll have fewer problems with wrap up and vice-versa. It is an important balance. Moving your differential forward or rearward on the spring can mean you upset the bias balance designed into your springs and an inch or two can make a difference.
