My two outermost screws are 60 cm apart. I think that's all I can do.

The wall rail is approx. 70cm wide with screw slots along the entire length (see product photo). 64 cm is therefore possible without any problems. The question is whether this is stable enough to support the unit. It is recommended that the screws be distributed over the entire width.

Take a look at the technical drawing. It says max 600mm