Can I replace a smoking, noisy and slowing 2008 R350 motor and transmission with 2012 motor and transmission?

What is your question?

My 2008 R350 smokes grey and black. 140,000 miles. It slows down and not picking up good speed especially when going up hill. it has this loud tick-tick sound from the motor. I have a used parts dealer friend who is taking a 40,000 mile motor and transmission from his 2012 R350 that was in wreck. Can I possibly put this 2012 R350 motor in my own 2008 R350?

How long has your 2008 Mercedes-Benz R350 had this problem?

6 months