Rebuilding of hammers will produce hammers of differing weights. Only by proper distribution of hammer weights will produce balanced rotors. It is not the individual hammers that require balancing, but the rotors themselves require balancing. The foregoing hammer distribution technique will produce fairly well balanced rotors, regardless of the number of rotors or hammers.
These rotors are within 0.5 lbs. of one another and will most likely be acceptable. If they are not within the 0.5 lb limit, rearrange a couple of hammers from each rotor to more closely distribute the weight. If this is not acceptable, select the lightest hammer in a light rotor and add weight by welding to bring to within tolerance. Color code all the hammers on any particular rotor. Vary colors for each rotor. When assembled on the rotors, assemble all hammers with a particular color to any given rotor, keeping all the same color hammers within a rotor.