The modifications of the GCS you seek are in the FIRST (not the current)
edition of a book called 'The Scientific Foundations of Neurosurgery' ed.
Crockard et al., published by Blackwell. They are not in the current
edition as I suspect they are not in widespread use, there are several
modifications for different pediatric age groups and thus lack the
simplicity that makes for ease of application.
C. N. Pidgeon