Heres the story

My buddy just bought a new used truck. The previous owner did a 4.3 to 5.3 swap. His truck is a 2002. Well his Nelson tune came in today and it wont start. Its not doing a security relearn, this im sure of. now my question. could it be that the engine is from say a different year model? Im sure the tune nelson sent out was a 2002 PCM. If the engine is from a 99 or 03 or something. Would the Nelson Tune for the 02 work with that motor? Is there a way to identify what year the motor is from? Like maybe the part number on the current PCM its running off of? Does anyone have a list of the year models and part numbers?