pulled the seat and tank on my 03 SXC and here are the numbers....
Tank - 584.07.013.100 11 liter tank
Seat - 58407140400 and below that 58407140500 and marked
"for 18L tank"
Hope that helps man, let me know if you want any more info as the bike is disassembled at the moment.
"Dakar must be a race for few people, Dakar is a dream, the dream of the Rose Lake, if everybody finish it, the dream is over" Fabrizio Meoni