you need adjustable uppers AND lowers that can adjust shorter than stock, in order to align your rear pinion angle.
set pinion pointing parallel with the driveshaft, such that there is a -1 to 0° difference between the two, at ride height.
while doing this, you need to ensure the axle is centered at full bump, with the springs removed, and proper bumpstop extensions installed. This means lengthening the uppers and shortening the lowers. You're not losing wheelbase. Adjusting uppers only will push the pumpkin back into the gas tank, create track bar interference problems and put the tire into the rear wheelwell.