Cut the parts to be used in the assembly. Else how are you going to assemble the new parts? :)

Remove all the internal of the original K40 laser cutter

Measure and make the holes on each side of the case

Install the lateral profiles on the case

Mount the Y stepper motors and idler on the lateral profiles

Assemble the X profile and mount it to the lateral profiles

Mount the X stepper motor and idles to the X profiel

Put the GT2 belts and adjust tension as needed