I dont know what was used in those kits, but I do know that 10% ammoniated mercury oint. was the USP standard in the United States in the 1930s. The 5% oint. was marketed but not a standard strength. Also the US Army Medical Supply Catalog lists only the USP Ammoniated Mercury Ointment item 91145 . So more than likely it was the 10% strength in those kits. USP stands for United States Pharmacopeia which is a legally recognized compendium of standards for drugs in the US.
Hope this helps until you get a better answer