Jentschura's "Warships of the Imperial Japanese Navy 1869-1945" has several photos of the W13 minesweeper class, they clearly show shielded single 4.7-inch guns so they are definitely correct. This publication is a must for modders, it has LOTS of photos and line drawings- not only of the major ship types and classes but also of the more humble ships such as minesweepers and other auxiliaries. My copy is dated 1977, though, so it may not be available any longer. However, I'll be happy to scan stuff provided you ask very nicely
