If your going to use the 04 ECU, there is no need to change the Intergrated body unit.
The 05 intergrated body unit is the emmobilizer unit too.
To use the 04 ECU in the 05 is a dirrect plug in,but you will need to move around some of the pin-outs on the 05 ECU harness. Fuel pump and a few other pin-outs were moved to prevent a thief from just plugging in a 04 ECU and driving away.
I have both 2004 and 2005 ECU pin-out charts.Send me a PM with your email address and I'll send them to you.