The problem with a A320 convertable is that I don't belive that one exists.
The 757 allready is factory available with a main deck cargo door and a conversion for is is also certified for it allready.
Then there is the long range issue which would be a valid concern for New Zealand.
Also a large number of 757's are going to be entering the used aircraft market (Thank you BA)
OBAMA-WORST PRESIDENT EVER....Even SKOORB would be better.