How to calculate the counter-wheight
A counterweight is an equivalent counterbalancing weight that balances a load. Its purpose is to make lifting the load more efficient, which saves energy and is less taxing on the lifting machine.
Counterweights are often used in traction lifts (elevators), cranes and funfair rides. In these applications, the expected load multiplied by the distance that load will be spaced from the central support (called the "tipping point") must be equal to the counterweight's mass times its distance from the tipping point in order to prevent over-balancing either side. This distance times mass is called the load moment.
A counterbalance is a weight or force that balances or offsets another as when two objects of equal weight, power, or influence are acting in opposition to each other. The objects are then said to be in counterbalance.
I made a test and by several adjustment I realize that the CW is 261 Kg.
Probably there's a formula that will calculate the part size to lift over the fulcrum and apply the equivalent momentum to the other size.
So I tried to remove the part negative to the rotation and show the center of the mass (Menu: View > Certer of The mass), then extiimate the distance from the fulcrum 2657.57 mm.
The momentum would be 51.55 Kg x 2657.57mm = 136997.7335 Kgfmm or 137 Kgfm approx.
The other side of the fulcrum there should be the same:
137 / distance_point_of counter_weight
137/ 0.521 m = 262,951503839 Kgf
Herein attached the assembly which I done the test. If you can use the simulator you may experiment for yourself