There is going to be one more letter after the basic part number 9425 (just about all intakes use this basic part number-the 9425), the C8 means it is going to be most likely for 68 and newer.C8AE-9425-A and C8AE-9425-D are the 68 390 GT intakes according to one of my books.
Is there perhaps a suffix at the end which is missing? Often that, along with the last letter of the first group, denotes a particular permutation of the main design and application.
For example, for a service part, a C8OZ-9424-B manifold would be an iron 2 4V intake for a 428 PI or CJ/SCJ engine.
I only have listings for service parts, not OEM, and the number you gave is not listed. The only two service part numbers with a "9425" in them are for 427's and both are C4 numbers. All the 390 numbers are 9424....