Assemble them,but don't fully torque them,just snug the screw.
Install the assemblies on the gun,but don't torque fully.
Run a 1" dowel through the rings to align them.Remove the rings,and fully tighten the screw holding the ring to the base.
Reinstall the bases.
I machined a 1" steel dowel just for aligning rings,feel free to borrow it if you need one to mount a scope.