Using 4,1 dual CPU tray in flashed 4,1->5,1 Mac Pro?

Hi,

I have a 4,1 flashed to 5,1 single CPU Mac Pro (3.46GHz).

Would an un-flashed dual-CPU socket daughter board from a 4,1 (e.g. 2 x quad 2.26 or 2.66) work in this machine, or does it have to be flashed to 5,1 first?

Does the flashing only affect the CPU board, or is it the whole logic board?

Thanks!

Ed