The National Bank has published a comprehensive study of the period from 1940 to 1971 in four volumes. You can download digital versions of these volumes below. 

• I. Herman Van der Wee and Monique Verbreyt (KU Leuven)
  Oorlog en monetaire politiek: de Nationale Bank van België, de Emissiebank te Brussel en de Belgische regering, 1939-1945
  (War and monetary policy: the National Bank of Belgium, the Bank of Issue in Brussels and the Belgian government from 1939 to 1945)
  Language: Dutch. Summary in French | Full text 
    
• II. René Brion (ULB) and Jean-Louis Moreau (UCL)
  La politique monétaire belge dans une Europe en reconstruction (1944-1958)
  (Belgian monetary policy in a Europe undergoing reconstruction)
  Language: French. Summary in French | Full text
    
• III. Walter Pluym and Olivier Boehme (NBB)
  Van de golden sixties tot de val van Bretton Woods (1959-1971)
  (From the golden sixties to the collapse of Bretton Woods)
  Language: Dutch. Summary in French | Full text
    
• IV. Isabelle Cassiers and Philippe Ledent (UCL)
  Politique monétaire et croissance économique en Belgique à l'ère de Bretton Woods (1944-1971)
  (Monetary policy and economic growth in Belgium in the Bretton Woods era)
  Language: French. Summary in French | Full text