this is probably one of the dumbest questions on this forum.. but will a 2.7 ecu work with a 3.5 motor?? simple yes or no.
Would it even start?

 

I swapped a used 3.5 pcm on my 3.5 and found out that it starts the engine ok and then it dies.
When changing an pcm (or ecu) they have to be programmed, (reflashed) with the proper VIN and odometer reading.
So the answer to your question is "no"