Myke, no the CI air cleaner will not fit your carb. Yes, you will need to switch to a 4bl or find an adapter to attach to the base of the air cleaner. And here is an extreme option that WILL work. Cut the 2bl hole from the bottom of your air cleaner ( or some other 2bl air cleaner) and weld it to the base of the CI air cleaner. Now folks, pay attention, I said "extreme". REGARDLESS of what you do or don't do, PUT THE CI HOOD ON YOUR CAR. It will become a different car!
As we speak, I am installing a complete CI system on a 70 with a 400smbk. The rubber seal around the air cleaner will be about 1in. further back than on a BB, so it will still mate with the hole in the hood just fine. From the factory, CI air cleaners had a spacer between the carb and air cleaner base, you will probably need some kind of spacer. Go for it! Good luck.