Michael,

Did the Cummins tech confirm that J1939 data is definitely present in the diagnostic connector and which pins? There's not too big of a difference between picking up the data on J1939 or J1587 except the J1587 gateway is $60 each more and you will definitely need two. 

As I see it you have three options right now:

• Buy two J1587 gateways  (YDES-04N) and pull data via the J1587 pins. We will need to identify these and likely you will need to tap into those wires.
• Buy one J1939 gateway (YDEG-04N) make the connection, and see if you get data for one engine or both. If only one, you'll need to buy another gateway.
• Buy two J1939 gateways, make the connections and see what you get. Even if both engines are on a single network you can always configure both gateways to work on the same network. The one advantage this gives you is some fault tolerance in that the failure of one gateway wouldn't take out all engine data.

Hope this helps clarify some. If not, please let me know what needs more explaining.

-Ben S.