The assembly you have is for a single carb unit. The holes at the north & south are to attach the lid to....have to buy studs and inset them into the base plate, use jams nuts to secure.
You are right, from the standpoint there is no place to attach it to the carb...that's the way they came. Buy a bolt to fit in the carb (where the threaded stem for the air cleaner would go, buy a short piece of 1/2" wide by 1/8" thick flat bar steel, drill a hole in the center for your bolt to pass through to the carb. You will have to bend the ends of the steel down so the bar will pass over the carb without interferring with the linkage...so just the ends pinch the bottom plate of the air cleaner down against the carb.
There is a bracket to do this, I just do not know who sells it. Like beachkid said, you can make one. Only instead of bending down, it is bent like this: -\__|__/-
The studs for the holes in the lid go through the flat part at the ends of the bracket. A short stud is used in the center to attach to the carb. Maybe Tony Branda has one.
No, it is bent down /----\ like this. It straddles the carb (left to right) and pushes down on the base to secure it. The cover studs just bolt into the base with a nut on the inside and outside. Don't forget flat washers to prevent damage to the fiberglass..
In response to them all being alike. The originals (68 Shelby) do have just one hole in the middle for the carb stud. Plugs were used for the other two holes. The ribbing is slightly different on the top plate whereas the bottom plate is thin metal with several ribs and a nipple on the back. Repos have pot metal tops and bottoms. Repo base plates will not work well with some Holley carbs.
1968 SHELBY SINGLE QUAD CARBURETOR INSTALLATION HARDWARE KIT FOR A OVAL AIR CLEANER: Includes 2 wing nuts, 2 studs, and 1 bridge for hold-down (attaches to carburetor to hold oval bottom in place) with carb stud.