Each primary strut is installed on the outrigger and the cross brace. The primary struts may not be perfectly right, what I did was simply to boil some water and plunge the struts into the hot water (not boiling any more). Then you have a few second to make it right again.
From Apollo 11 onward the +Z landing probe (corresponding with the landing gear with the ladder) was removed. That decision however was taken at a very late stage and for that reason the probe locking mechanism is still present on the +Z primary strut on Apollo 11 and 12. It disappears from the +Z primary strut from Apollo 13 to Apollo 17. Make sure then to remove that part with a precision knife.