Which Box for distribution code would I fill out? I did not receive a 1099-R and it will never be provided since the income is from self-employment (United Nations).

The UN tells employees and ex-employees to fill out box 5A (and i assume to add it to 5B for taxable amount) on money withdrawn from the Pension Fund. As UN employees, we fill out 1040 forms and Schedule SE (Form 1040) for self-employment tax. I am unsure if this means I should avoid the 1099-R as tax was not withheld at all.