Now I don't feel so bad. I'm in the middle of the same project. I will take and post pics.
8mm tap, 17/64 drill bit
I am drilling a hole, tapping it, threading in an 8mm stud and if there is enough room behind the plate, backing it up with a nut and loctite. If not, just loctite. My only concern is that there won't be enough threads to reliably hold the stud without a nut on the back side.
The other option is to put some jb-weld behind the plate and screw the stud into the plate and jb-weld.
1967 230SL Havana Brown Auto with A/C