I then took the slug and placed it into the plate to complete the circle.
All welded up.
some flat black.
I had to round out the hole in the firewall a little larger to make the large nut fit through on the back of the plate. I also had to drill 2 holes into the plate to make the bottom 2 studs fit. But it's in and works great!
Now to hook up my lines. Thanks to my local Parker store for making me some lines that adapt from the standard fittings on my power steering pump and steering hear to the metric fittings on the booster.