It looks like you have a 1963 intake manifold, which was not used on any Mustangs. What is the casting number on the front of the manifold?
To answer your original question, the 1975 Ford Car Parts book has the following part numbers listed:
- C7OZ-6A666-A (Motorcraft EV-42) - PCV valve in line with the hose and fitting.
- C2OZ-6A631-A (Motorcraft FA-58) - Element/crankcase ventilation oil separator.
- C2OZ-6A633-A - Retainer, crankcase ventilation oil separator element.
The fitting is called 'Adapter assy, Crankcase Ventilation, p/n C3DZ-6A665-B.
The remaining part numbers are for the fitting, which you have, and bulk materials and hardware. But, it appears that you are missing the PCV valve as well.