Looking at our unofficial registry here:
https://docs.google.com/spreadsheets/d/10qylpOcZgQLu9SAvhtRhmjGS8Cg0B_y0MpJSU-poATk/edit#gid=370348491
I see that Jeff Tepper has an early November, 1968, San Jose build - very close to your build date. Jeff is a regular poster over on concoursmustang.com. I suggest joining that forum and sending Jeff a PM about where his decals are located. I'm sure he'd be glad to help. It's almost assured yours were in the same place.
As an aside, my car is a June 1969 Dearborn build and has the engine spec decal on the passenger side inner fender. Nearly all cars built in Dearborn have it on the drivers side. It turns out there was a 2 or 3 month period where someone (ones?) at the plant did this and it's been documented. The other 10 zillion cars they made there had the decal on the drivers side. I know, I'm a geek.