Ah, the first Barnard designed Ferrari, sigh.
Very nice kit, I built close to 10 years ago
The reason the headrest was a seperate part was because of the shape. Think of the way the molds fit together and you'll realise it would not be possible to mold the wholle thing with a two part mold and have it eject cleanly. These days Tamiya use multiple part, sliding molds but they are more complex and expensive.