If you have math showing that they could come up with more than 28% of the money to pay for European imports (specie excepted) then I will be glad to take a look at it.
But it seems axiomatic to me that if you produce 28% of the export value, you will only be able to pay for an equal import value.
I have the fact that without southern exports tariff income increased markedly from 1863 onward. You have your convoluted math and asinine conclusions.