I found on the net some photos of the WWI stuff from Warsaw Polish Army Museum.
several guns, in the bacgsound is the barrell of the Russian heavy siege howitzer (link to the photo of the whole gun was posted on thins forum some time ago, it was Russian museum website). From the front: Russian 3 inch with long barrell, 2 Russian mountain cannons, 75 mm Schneider, British 60 pounder, Russian or French heavy mortar (220mm?)
Mine-throwers, Austrian Borell and German (Rheinmetall?) Heavy shells in background are WWII ones.
Borell mine-thrower and British cannon (60pounder?)
The 75mm M1904 Schneider is a rariety! This was the principle French export gun that competed with Krupp in the arms market before the Great War. It was bought in large numbers by both Serbia and Bulgaria, and became those countries' primary divisional gun. It did equipt some batteries of French Horse artillery at the war's outbreak, but they were later given/sold to Belgium... where one survives today in the Royal Army Museum @ Brussels .