Mccartercar

Hello,
I recently picked up a 2003 A6 Quattro 3.0 some time ago with around 117,000 miles on the vehicle. It had severe damage to and pillars where it had ran under a tree. I'm gonna say its unrepairable but it drives great and the drivetrain has been well maintained.
Today I bought a 2004 A6 Quattro 3.0 with a broke timing belt/water pump for the donor body. Unfortunately I missed the minor detail that the 04 was made after VIN 018001 and therefore was different than my 03 3.0 motor, at least as far as heads and block. Initially, I used the AVK ident found on both but later found out there's more to it.
Hollander says, the intake, manifolds, k frames, and transmission, at the least, are the same. It says the block, heads, and ecm, that I checked, are different. So, would the 03 3.0 pre 018000 vin motor work in place of the 04 3.0 post 018001 vin if I simply change the ecm along with the motor?
Is the ecm pinout different on the two?
Is the wiring harness different on the engine?
If the ecm switch did work would it require being flashed in some way for the security system and key to accept it?
If it wasn't could I simply change steering columns too and use the key from the 03?
Thank you very much for taking the time to read this and I appreciate any answers and/or knowledge of what I am about to embark on.

Mccartercar

Hi,
I thought I'd post an update. The motor from the pre 018000 vin (03) worked in the post 018001 vin (04) body. The only thing I had to change was the ecu, I brought it over from the 03 and everything went well. So Hollander was right that it's a different motor, but only internally and how the computer is programmed for it, everything else was exactly the same.

N_Jay

Congrats!