Z axis top brackets, of P3Steel, differ between v1.x/2.x and v4
I've just seen this right now, I'm Alvaro Rey, the designer of the p3steel v4 mod. The change was made, because with previous versions with the extruder homed, if you go up in the Z axis, the extruder motor could hit the Z axis top plate. So, in order to avoid that, I just changed the design.

The bearing in the z axis is not necessary but some people prefer to use it, in order to avoid wobble in the threaded rod. 

Anyways, I designed a printer part to fix the bearing in the Z top plate.