I have a 94 Disco and I was told by the PO that he had a 4.0 installed by the dealership. How do I tell if this is really a 4.0 or if it is a 3.9? The reason I ask is because by serpentine belt tensioner pulley crapped the bed so I need a new one and a new belt and I want to make sure I order the right parts. I am pretty sure the the 3.9 serp belt and the 4.0 serp belt are different but maybe someone can correct me if I am wrong. Thanks in advance for the help!