FYI: from /usr/include/types.h

/* typedef for the File System Identifier (fsid).  This must correspond
 * to the "struct fsid" structure in _ALL_SOURCE below.
 */
typedef struct fsid_t {
#ifdef __64BIT_KERNEL
        unsigned long val[2];
#else  /* __64BIT_KERNEL */
#ifdef _ALL_SOURCE
        unsigned int val[2];
#else  /* _ALL_SOURCE */
        unsigned int __val[2];
#endif /* _ALL_SOURCE */
#endif /* __64BIT_KERNEL */
} fsid_t;

And, currently I am building in 32-bit mode, with a 64BIT kernel (AIX 6.1) - so I expect it to be 2 unsigned_longs.

However, I am not smart enough to find a solution: I tried:
    PyStructSequence_SET_ITEM(v, 10, PyLong_FromUnsignedLong((unsigned long) st.f_fsid));

and     PyStructSequence_SET_ITEM(v, 10, PyLong_FromUnsignedLong((unsigned long *) st.f_fsid));

Both return:

"./Modules/posixmodule.c", line 9328.80: 1506-117 (S) Operand must be a scalar type.