FWIW, the first draft script of "Spock's Brain," dated 6/11/68, is virtually the same as the revised final draft script dated 7/1/68 (with change pages to 7/5/68, the Friday before the Monday filming). Major differences between the two versions include:
1. Spock's body remains behind in sick bay.
2. In the first draft, Kara states that the use of Spock's brain was preordained. In Act IV, while she holds the phaser on Kirk, McCoy, and Scotty, she says:
KARA
Twenty generations ago the moulding of the
controller was begun.
His time of birth was determined. His body
was only the vessel of germination.
Now he is ready for us.
Additional dialogue follows after this between Kirk and Kara where they discuss the "ancients" and the commandments.
3. The pain belt bands in the revised final draft are pain headbands in the first draft.
4. The scope of what Spock's brain was controlling was made clear with this scene in the first draft:
POV - WHAT THEY SEE (MATTE)
A huge incredibly complex mass of vast machinery of alien design, filling a cavern which might reach for miles.
SCOTT
Incredible design, Captain.
But I recognize some of it. Air recirculation, heater,
hydroponics regulators... all life support...
the work of genius.
Their eyes come to rest on the black box atop its pedestal. Light rays stream from it to all sections of the great panel.
Interestingly, this scene survived in the revised final draft but was truncated substantially. However, it wasn't filmed.
5. The surgery to reinstall Spock's brain is done in sickbay on the Enterprise.
6. The tag, which takes place on the bridge, includes not only more jokes about McCoy's surgical errors but also this sidesplitting exchange:
KIRK
I am not given to predictions, gentlemen, but I venture one now.
That conflict on the surface will be a very short one.
SPOCK
I fail to see what facts you base that upon, Captain.
KIRK
Long, cold winter nights, Mr. Spock...
and the fact that cuddling is much warmer
than sitting in front of a fire.
SPOCK
Cuddling, sir?
McCOY
A human habit, Spock. We don't expect you to know about it.
SPOCK
Of course not, doctor... since it is a well known fact we
Vulcans propagate our race by mail.
