OK, I picked up a different air cleaner decal to add to the discussion. It's similar to the first one, but adds the air cleaner part number and replacement filter part number.
There are a few lines of discussion on this one:
1) Is this decal accurate in and of itself? The air cleaner part number if C8OF-B, which is the '68 S code GT air cleaner with round vacuum motor and chrome lid. See the '75 MPC listings. However, the same MPC lists FA-50 as the replacement filter, and the decal is showing FA-74. The MPC shows FA-74 for an entirely different application. I believe the decal is erroneous.
Update: I forgot to mention that I measured an air filter (aftermarket) that I have in my C8OF-B air cleaner. It measures 2.8 inches tall and fits properly - the lid is sealing on the top of the filter (the snorkel is off so I can see it making contact) and the lid gasket is sealed on the edge of the base. The height of this filter matches what's listed in the MPC for an FA-50.2) Was this style of decal (with different part numbers) used on '68 SJ engines?
3) If so, what was the usage compared with the generic Autolite decal? In other words, were they used at different points in the model year, would they
both have been applied to a single air cleaner, etc.?
For reference, Dudley posted a photo of what appears to be an original decal of a similar design from his SJ 289 in this thread:
http://www.concoursmustang.com/forum/index.php?topic=4715.0