Correct about the carbs being mounted backwards. They were originally built to be one of several choices of intake styles that were used on the Miller front wheel drive Indy cars that had their engines mounted backwards in order to mate to the front wheel drive transaxle set up.
When used in a FWD Miller, the carbs were actually facing the correct way.
The one with D shaped carb bases denotes it being an original one. The intakes with the kind of triangle shaped carb bases were repopped sometime in the 50's.
That single barrel air cleaner is not one of the original designs. Neat though...