Add 2 Light Bluish Grey Minifig Hands and 2 Dark Bluish Grey Minifig Hands.
I add a "stand" in the building instructions if you want to secure the stand-up position of the walker. Its LDD File is available here : https://drive.google.com/open?id=1oxfIQpj5dtKKLhdCsSarKfjR5CaPReyk
If you have some remark or problem with the instructions, let me know and I will correct. Don’t hesitate if you have questions! And if you have improvement to propose... ;)
Moreover, could you post pictures of yours when you finish to build it and write a comment below please? Thanks ! :)