BEnji, you're missing one piece from the bracket / surround. What you have is the "bottom"...the rad sits down into that and there is another u-channel piece that slips into what you have and there is a bolt on each end to sandwich it together. FYI there are little strips of rubber between the end tanks and the bracket / surround /support thing. Looks like the rubber strip that goes down the center of a spoked bicycle wheel.
FYI, it's starting to look like a car, I know it's got a long way to go, but still super excited for you.