While visiting fort the Loncin (Liege) a few weeks ago (the visit is very good and some turrets are more or less in place, unique for the wwi forts of Namur and Liege.) The guide told me that a group is building for the fortress museum and exact as possible replica of the 42 cm Bertha mortar. The main source apart from photograhs is the rather large scale Krupp model possibly used in building the real thing of the mortar in the Musée de l'Armée in Paris.
