I bought the ARB from Garrett and Bruce from Overland Experts. Thanks for the referral Matt!
Does anyone have extra captive nut plates like in the attached? These are what the vertical bolts screwed into. They clip onto the frame where the bolt holes are located. As you can see in the pic one clip is broken.
Edit* ARB's website has fitting kits but not for a Defender. They don't show pics so can't see if they are still usable.