Why would one touch the pinion to install an ARB?
Installing an ARB necessarily requires replacing the carrier, since the ARB is, in essence, an entirely new carrier assembly. Installing a new carrier requires dismounting the ring gear. Dismounting the ring gear requires a new ring gear/pinion preload set up. Machining differences can't be accounted for, and you have to assume the new carrier won't be the same as the old one.
Consider an ARB installation as a complete differential overhaul, and set up everything as new, including side load on the bearings, pinion depth, and pinion crush if so equipped.
As a result, ARB installations are generally considered to be something for professionals, and are not in the same league with installing a typical "lunch box" locker which requires only replacing the spyder gears, leaving bearings and ring/pinion relationships intact. Best bet is to take your new assembly to a reputable shop and have the installation verified.