The easiest way at this point to identify the engine is to check the bore. If it is 91mm then it is a 3.6. They will also be a flat top piston. The block will have a AMG36 stamped below the engine number. As far as the head goes. I would just check the cams. I think there is a little port work done on the exhaust side from memory. The intake cam should be a amg part and should have more than 50mm from the base circle to the tip. Stock m104 lift is 8.9mm the 3.6 has close to 10mm of lift.