How much weight does a thrust reverser add?
For the LEAP-1B example, the weight you found is a dry weight that does not include the reverse system per the type certificate. Such weights are very hard to come by, even from the respective system manufacturer. However, statistical data can help.

According to NASA, the reverse system of a GE90 class engine can weigh upwards of 30% of the nacelle weight.


  [Studies] conducted by General Electric Aircraft Engines
  indicate that the thrust reverser system accounts for more than 30 percent of
  the nacelle weight (not including engine) for an engine having a fan diameter in
  excess of 100 inches. This could be as much as 1500 lb [680 kg] for a GE 90 class
  engine.


As for the nacelle, an older NASA paper says the weight is in direct relation to its surface area constructed from simple cylinders.


  [For the nacelle, the surface] area is used to correlate weight, and, rather than introduce
  the complexity of the actual nonaxisymmetric shape of the nacelle, simple
  cylinders are assumed, using the fan diameter, the turbine diameter, and the
  lengths from the previous section.
  
  [And] a unit weight of 17.1 t o 19.6 kg/m2 appears reasonable.


From the same paper, here are some examples for the weight of the reverse systems of different engines:



Since the CF6 days manufacturers were able to reduce the weight of the nacelle and its components due to the "extensive use of composite materials."