@sr41 , you are making this extremely complicated. forgetting the KISS principle.
All you are liable for is to pay taxes on a pension /annuity distribution at your marginal rate.
However, if you are convinced that you must follow your path, I would strongly suggest you seek professional help --- a tax professional; / tax attorney whom is familiar with international taxation. Perhaps you also need to familiarize yourself with Tax treat between US and your "payor" country.
Good Luck
pk
