We do not offer a 400mm extension enclosure as a spare. We only offer the MG6CEX which is 200mm height, you will need to use 2 of these to give the 400mm Height, these can be double stacked. MG6CEX can only be fitted to the MG2C# ,MG6C# and the MG8C# boards. MG6CEX cannot be fitted to the MG25C# and the MG16C14 boards