In addition to obtaining the basis worksheet (which is essentially the same as the Form 7203), gather up your prior Schedule 1120S K-1's. The K-1's won't show your initial and additional capital contributions but you should have those through your stock records or annual corporate reports if you have to file those each year in your state. The K-1's will show you all the basis additions and subtractions (including non-deductible ones) and distributions. Of course, this assumes the K-1's were properly prepared each year.
As to your shareholder debt basis/loans, this should be easier to complete since loans don't have the permanency of stock basis. I think you could concentrate on loans that were just outstanding as of the start of the year. For old time tax preparers this task will bring back memories of doing basis studies for mutual funds with years of reinvested dividends before the brokerage firms provided this data.
mtzttax
