The handicapper has been unable to split French stars Americain and Dunaden as joint top weights for the $6 million Melbourne Cup at Flemington on November 6.

The past two winners of the world's richest handicap will be carrying 58kg in the 2012 edition where they will attempt to carve a unique piece in racing history.

The French-trained pair will arrive back in Melbourne on September 29 bidding to be the first internationally-trained horse to win Australia's greatest race twice.

Only five horses have won the Melbourne Cup on more than one occasion led by the great triple winner Makybe Diva (2003, 2004,2005). The others have been Think Big (1974/75), Rain Lover (1968/69), Peter Pan (1932/34) and Archer (1861/62).

Since 1972 when the Melbourne Cup entered the metric era, 36 horses have carried 58kg or more with only Makybe Diva under 58kg in 2005 and Think Big with 58.5kg in 1975 being successful.

American and Dunaden have been handicapped with 9kg over the limit weight of 49kg, but with only two three-year-old entries allotted the minimum the spread in real terms stops at 50kg which will again raise the question of whether the weights are being too compressed in favour of the many northern hemisphere entries.

Racing Victoria General Manager Racing Greg Carpenter is responsible for the weights and maintains Americain and Dunaden face a formidable challenge.

The allocation of 58kg to both Americain and Dunaden represents a significant challenge to both horses given only two horses have carried that weight or more to victory in the past 40 years, Carpenter said.

Dunaden won the 2011 Melbourne Cup with 54.5kg and he rises 3.5kg. This is the same progression Americain made after winning in 2010.

Americain ran an outstanding fourth behind Dunaden last year with 58kg when beaten just under 1.5 lengths and he takes the same weight this year.

Since last year's win Dunaden has added the G1 International Vase in Hong Kong to his record.

Only Empire Rose (1988), Gold And Black (1977) and Carbine (1890) have won the Cup after finishing second the previous year so Red Cadeaux will join one of the most select groups in Cup history if successful, Carpenter said.

Carpenter had to deal with 14 international horses that are not entered for next month's Caulfield Cup after issuing weights for that race on September 4.

Those notable entries include three from Ireland's dual Melbourne Cup-winning trainer Dermot Weld led by last start Ballyroan Stakes winner Galileo's Choice, who entered quarantine in his homeland last week and looks well in with 53.5kg, the same weight as last year's Caulfield Cup runner-up Green Moon.

Galileo's Choice is a very progressive horse that has a similar profile to Dermot's first Cup winner Vintage Crop (1993) in that he's been successful both over the jumps and on the flat, Carpenter said.

The powerful Godolphin stable, who have been attempting to win the Melbourne Cup since 1998, have four entries.

Ascot Gold Cup winner Colour Vision is the highest weighted on 55kg with Cavalryman on 54kg, Lost In The Moment on 53kg the same weight he carried to sixth last year and Ebor Handicap winner Willing Foe on 52.5kg.

Willing Foe did not help his chances of qualifying for a start when he finished third in France on Sunday.

Willing Foe emerged as a Melbourne Cup contender when winning the Ebor at York last month, where he defeated subsequent Irish St Leger winner Royal Diamond," Carpenter said.

"However, with 52.5kg he will be vulnerable in the ballot, Carpenter said, pointing out that horses on 52kg filled the final positions when the final field for last year's race was declared.

The nine-year-old Efficient, who won the 2007 Melbourne Cup under 54.5kg, is the other past winner being aimed at this year's race. The Robert Hickmott-trained veteran has 55kg.

No southern hemisphere nine-year-old has ever been placed in the Melbourne Cup, Carpenter said.

Australia's newly-crowned champion middle distance champion More Joyous won her 20th race last Saturday but is yet to race beyond 2040-metres which makes her 56kg a serious assessment.

She has not yet passed the ballot and the only mare to carry more weight to victory in the race is Makybe Diva who carried 58kg in her third Cup win, Carpenter said.

The ruling favourite Mount Athos, unbeaten in three UK starts for trainer Luca Cumani, has 54kg while Peter Moody's crack import Manighar, winner of three G1 races since finishing fifth in the 2011 Melbourne Cup under 54kg, rises to 57kg.

The Australian-owned American St Leger winner Jakkalberry has 55.5kg, 1kg more than 2011 Caulfield Cup winner Southern Speed, who is yet to race beyond 2400m.

Sanagas, the German-bred G1-winning import, is the highest weighted of nine entries for 12-time Melbourne Cup winner Bart Cummings with 54kg.

Ethiopia, the ATC Derby winner in April, is the highest weighted four-year-old with 53.5kg while Sydney Cup winner Niwot, who was the first Australian-bred horse home in last year's Cup when eighth, rises from 51kg to 53.5kg.

First acceptances for the Melbourne Cup will be taken on October 9.