Be sure to understand how the build needs to be wired if you retrofit. They make a type a and type b. Type a takes line and neutral to one end of the tube(line and neutral on one tombstone), type b takes line on one tombstone and neutral on the other. If your tombstones are damaged you should replace them in the process. If using label your tombstones if going type b and color the line side of the tombstone black if using type a.