7 1/4 to 8 1/4 swap

Higher than stock springs will decrease the amount of slop at ride height assuming the distance from the locator pin on the spring to the front spring pivot is the same. The slop is at it's maximum at the stock ride height and will decrease as the suspension extends or compresses.

The radius of the arc that the axle travels in is much smaller than the radius of the arc the drive shaft follows. This makes the distance from the axle to the front u-joint less at the extremes of the travel and pushes the slip yoke into the tranny more at the extremes reducing the slop.