Treatment of incomes

both of them will be shown as indirect incomes, because they are incurred after doing the sale.  As you show VAT to be paid by the firm under the indirect expenditure after taking the set-off of VAt paid, same way duty drawback will be shown as deduction from the duty payable & net amount will be debited as an indirect expense to the P&L.

For gain arising on exchange difference it is not an direct income to the firm as the sale is already being recorded previously.  So the realisation of the sale would be an indirect income if there is an gain.