They are interchangeable going backwards but not using a older block in a LML truck.This may help. I am pretty sure any block up to 2016 LML are interchangeable.
Not sure if this has been listed anywhere as a sticky or not but thought it might be worthy of one. If it has been covered before I appologize. I think it would be great idea to list what stock parts can be swapped over from one generation of Duramax to another to get performance increases that...www.duramaxdiesels.com