The Skyjacked springs (mis spell intended) may come with shims but remember those were designed for a 4x4 which uses a slip shaft type driveshaft. The slip shaft will be a two piece splined d-shaft that will use a CV at the t-case end and a u-joint at the axle end. The proper geometry for this type of shaft is the axle pinion and d-shaft are inline so that the u-joint runs with very little to no angle. The shim turns the axle up to line up the pinion and d-shaft. You don't want this. Your slip yoke design uses two u-joints (one at each end) If the u-joint up at the trans is operating at 10 degrees, the u-joint at the rear should also be running at 10 degrees. This is due to the inherent problem with the u-joint design that as the joint operates at an angle, it produces a vibration. (the more angle there is, the more vibration it produces) A second u-joint on a common shaft, operating at the same angle will cancel out the vibrations of the first. When there is a CV included in the d-shaft, the CV is essentially two u-joints connected to each other, therefore the vibration is cancelled. This also means the u-joint by the axle has to be set with little to no angle or the pinion should be inline with the d-shaft (no angle = no vibration)
This illustration shows you the proper d-shaft geometry for a slip yoke, two u-joint d-shaft and you'll need to shim accordingly
Isn't it the Chevy springs that are 52" long? In any case, longer springs theoretically ride smoother than shorter springs. Yes there is a 4 inch difference in length. Whenever a leaf spring flexes, it's overall length changes. To accommodate this difference in length, a shackle is part of the spring design which allows for the fore and aft change of length. If you add a longer spring or a highly arched spring, the shackle should allow the spring to fit, but there can be reasons to change the location of the shackle, such as when the shackle doesn't provide the needed length change.
Other than the spring, the suspension itself hasn't changed. It will still have the same amount of wheel travel from full stuff to full droop. Going with a longer spring will change where in that travel the vehicle will come to rest at. The ride will still be dependent on how soft or stiff the springs are. The other aspect will be how far will the suspension travel before reaching it's limit. Having spacers and longer springs will obviously place the suspension near it's downward travel limit, so if there is only, say, an inch of down travel left, and say you roll into a 2 or 3 inch deep pot hole on one side of the truck, the suspension on that side will drop an inch and make contact with the bump stop and the tire will be temporarily airborne. Is it ideal? Not really, I would recommend having a bit more down travel available, to help keep the tires on the ground as much as possible.