We all know that the US Federal government ran on Tariff revenues in those days. Tariff's were collected on Imports, which directly correlate with Exports.
From my calculations of the export value of Southern products, (from the previously posted excerpt above) they make up 72% of the total. The citizen population of the North was 21 million, and the citizen population of the South was 5.5 million, yet those 5.5 million were furnishing 72% of the revenue to run the US Government, and from what you have listed above, apparently the US Government was putting a lot of coins directly into a lot of Northern pockets as well.
Of course it was the slaves who were actually producing most of the products for export, and the US government was content to allow 72% of it's income to be produced by slave labor, and the Northern Protectionists were content to receive the benefits of this slave labor as well.
They only reacted with fury when they realized that income stream was going to be cut off from them.
50% is more realistic for 1860.
Your higher number might well be realistic for prior years, but by 1860 other US products, especially manufactured, also were growing rapidly.