Western Star DD15 To Cummins

[Truckdriven]

I like to take on challenges and learn new things but I got myself in a little deep now, helping a friend who bought a 2009 western star dd15 with a scored cylinder. He decided to replace it with a 2006 cm870 ISX my part in the project is to get all the electrical figured it out. I have diagrams from the Detroit engine side and the Cummins and connected the wires into the cab plug according to the diagrams. My question are on the can bus communication, how do I confirm if the Detroit used j1587 protocol or j1939? There are both in the plug labeled as a spare with resistors in the end, then there is a third one that went to the Detroit but the diagrams don't say what protocol they are.

Also for the multiplexing on the Cummins side is that only possible through j1939? The truck has no throttle position wires to the engine so I assume this would mean that's done on the can
bus

Another problem, I am not able to get a connection to the engine through the truck diagnostic plug but can connect to the truck side.

I'm thinking there has to someone with some experience in this work that is thinking how easy it is....