Regarding Ford part# 5415, identified as INSULATOR- FRONT SUSPENSION SPRING- RUBBER, I thought I would post some pictures of what I think are original parts from my car, as well as a comparison to Ford NOS parts.
In the first picture you can see the full engineering part number, C4DA-5415-A.
The Ford NOS parts have stickers identifying the parts as C4DZ-5415-A, but the part number is not part of the rubber at all.
As far as a comparison of the original vs. NOS parts in general, the look and flexibility are indistinguishable.
The fourth position (usually) of a Ford part number indicates the design department, procurement and/or control of the part number. Letters "V", "Y" and "Z" are reserved for dealer serviced parts, the "V" is Lincoln, "Y" is Mercury and "Z" is Ford. The majority of the other letters are assigned to different engineering groups that designed the part or to special uses, "X" experimental. After the car is built and sent to a dealer, parts needed are identified with a "Z". You order a part from a dealer with a "Z", the box is marked with a "Z", it's stocked with a "Z" and sold it with a "Z". What is inside the box, the actual part, may be marked with the original engineering number, or not marked at all. This is normal. Ford sold cars, not documents. This entire scenario is to service cars with something that works, not to insure that a concourse grade part is used. Over time, parts change, different sources, different Ford service management. Also remember that by regulation, a car or truck manufacturer is required to supply parts for ten years minimum. It's the restorers who are left figuring out, did I buy a NOS part, or something in a box that works.
Jim
