This is a new, reproduction Delco Ignition Coil, Part # 1115261 for use in 1966 427-390 HP w/automatic transmission, and 1966 427-425 HP mid to late production, with Transistor Ignition.
These coils are brand new licensed GM restoration parts. They have the raised lettering on the case and the Delco Remy logo on the top. These are a welcome addition to vehicles with either the wrong part or a "just plain tired" coil.
Many other GM vehicles use this coil, too. Check your books!