At the top of structs.h (
    github.com/tbamud/tbamud/blob/master/src/structs.h#L40
 ), this bit allows you to alter them all in one place:
Code:
#if CIRCLE_UNSIGNED_INDEX
# define IDXTYPE	ush_int          /**< Index types are unsigned short ints */
# define IDXTYPE_MAX USHRT_MAX     /**< Used for compatibility checks. */
# define IDXTYPE_MIN 0             /**< Used for compatibility checks. */
# define NOWHERE	((IDXTYPE)~0)    /**< Sets to ush_int_MAX, or 65,535 */
# define NOTHING	((IDXTYPE)~0)    /**< Sets to ush_int_MAX, or 65,535 */
# define NOBODY		((IDXTYPE)~0)    /**< Sets to ush_int_MAX, or 65,535 */
# define NOFLAG   ((IDXTYPE)~0)    /**< Sets to ush_int_MAX, or 65,535 */
#else
# define IDXTYPE	sh_int           /**< Index types are unsigned short ints */
# define IDXTYPE_MAX SHRT_MAX      /**< Used for compatibility checks. */
# define IDXTYPE_MIN SHRT_MIN      /**< Used for compatibility checks. */
# define NOWHERE	((IDXTYPE)-1)    /**< nil reference for rooms */
# define NOTHING	((IDXTYPE)-1)    /**< nil reference for objects */
# define NOBODY		((IDXTYPE)-1)	   /**< nil reference for mobiles  */
# define NOFLAG   ((IDXTYPE)-1)    /**< nil reference for flags   */
#endif
 
Change the first line to something that fits your scheme
Code:
# define IDXTYPE	u_int          /**< Index types are unsigned ints */
 
Or similar.