Very interesting to see this. I have also been searching for one myself, and assumed that it was a generic fitment to mustangs that came from the factory with Holley carbs, but I haven't been able to work out which one it was, as my searching always seems to end up showing something not quite right, with a steel small diameter elbow on them. If you find out what other cars had this, then please let us know. Or if you work out where else to get one, maybe as a newly manufactured item, then please let me know.
As a substitute, I am using the stock Ford aircleaner that came on the earlier Panteras, and I have a short spacer to lift the aircleaner up so it clears the carb. It all fits under the stock engine covers and appears original. A question about the one you show in the photo - does it have space for the EGR canister thing at the back of the engine. The cover you show has a large recess, but that is for the distributor cap, right - the little tounges in the centre where it fits on the carb go to the engine front - and thus the snorkel would seem to point to the front on the one you show - or is the aircleaner mounted the other way around?
Cheers, Tim.