...
Centerlink Spacer Welding:
Mark the spacer (#2) so it's centered in the mating hole of #1, then give to welder for welding.
follow Rack Extension/Centerlink Welding Jig guide.
Place #5 through the hole of #2, then place #3 and #4 in the correct order onto #5 and secure with #6 on the back, do this for both sides. Torque to spec, ~25Nm.
Done
...