If this is your Dell: http://www.newegg.com/Product/Product.aspx?Item=N82E16883155176
...it has a std. mATX motherboard in it. It would be highly unprofitable for Dell to design a case that used proprietary MBs.
The only difference I see is that the OEM board is a full width while the MSI is a shortened width. But that is no issue.