Eric M. said:
Your question is a little confusing. You realize that the new arm goes on the passenger side, not the drivers side where the stock arm is?
Call the company, but I think you will remove the spring cap on the passenger side, install the studs, place the arm over the new studs, place the disk on top of the existing spring (it's a spacer to make up the difference of the new steering arm) and reinstall the cap on top of the new arm over the spacer disk.
OR
If the arm will fit over the existing cover (like the Rock Stomper unit), install the studs, put the arm over the cover and install the nuts .... but if this is the case, I'm not sure what the disk is for. You'll know if this is the incorrect method if the arm won't fit over the spring cap.
You can leave the existing steering arm on the drivers side in place if you'd like.
I'm assuming you know, but you will need a 2wd steering box or replace the sector shaft in your 4x4 steering box with one from a 2wd box. Then, install a special pitman arm. I didn't see it in the picture, so, I thought I'd mention it.
Eric M.