A 20 kg load sits 150 mm outside the guide. What does this mean for the bearing blocks?
Draw the free body first
Draw the forces, their points of application and the reaction directions. Choose a clear coordinate system. A load outside the support plane creates a moment; a bearing block is then loaded with more than just a vertical force. Also consider acceleration, cable-carrier resistance and external process forces.
Make the moment concrete
With g = 9.81 m/s², 20 kg produces a weight of 196.2 N. At 0.15 m distance, this creates a moment of 29.43 N·m. In a simplified planar model with two support points 0.20 m apart, this moment produces an additional force couple of 147.15 N. Add this contribution, with the correct sign, to the direct load distribution.
Stiffness and mounting are part of the choice
The real load distribution depends on block spacing, rail spacing, preload and frame stiffness. A stiff guide on a flexible mounting plate does not make the system stiff. Provide accessible mounting surfaces and decide how you'll set parallelism without pre-stressing the system.
Assumptions and applicability limits
The example is a static planar equilibrium model. It is not a life or load-rating calculation. For the final selection, use the load model, equivalent load and mounting instructions of the chosen manufacturer.