Oatmeal- do you mean Numrich sent you the wrong item? I'd be on the phone to them asking them to send you a n/c correct part...you did order the No 4 mk 2 part right?
On my No 4 Mk 2 that I just posted pics of with the C1 flash hider, I ended up keeping the sporter forend and cutting down the top wood to fit it since it was that different mk 2 setup and I also didn't want to butcher a Mk 1 piece to fit...