I updated my patch against Python3 trunk. I fixed my patch to pass 
most long and struct tests:
 - fix byte array import/export
 - check for overflow
 - compute exponent in conversion to a float (use PyLong_SHIFT=1)
 - fix formating to support 0b, 0o, 0x or custom base (XX#...)

You have to add "-lgmp" to LIBS variable of the Makefile.

There are still some issues about (unsigned) long long: overflow is 
not detected. mashal is broken for long.

diffstat py3k-long_gmp-v3.patch
 Include/longintrepr.h |   49
 Include/longobject.h  |    3
 Modules/mathmodule.c  |    6
 Objects/boolobject.c  |   12
 Objects/longobject.c  | 3053 
+++++---------------------------------------------
 Python/marshal.c      |    9
 Python/mystrtoul.c    |   26
 7 files changed, 376 insertions(+), 2782 deletions(-)