[TimG]

I don't have a problem with the "O's" or even the inverted "8", I've got plenty of examples of those in my files. The over stamp is a bit unusual and pretty messy. I'd look real hard for 435 signs on this car. No pictures of the tach, oil pressure gauge, four bolt main (big oil cooler plug), or transistor ignition stuff.
These would help verify its 435 heritage. Could it be a 390 horse motor with an over stamp from the factory? Could it have been over stamped later in life? I don't know. Too bad they had to pull the motor and rebuild it, with a strange stamp and no paperwork, you'd love to see the motor in its original, never removed condition. They should have documented the motor before removal if nothing else.