I to am converting to my 88-98 2wd Chevy Dually to 4wd and dropping a cummins into it, only a 12 valve! I am using a 1998 Dodge dually Dana60 front and it seems to be going pretty good so far. I have all the brakets made to mount the links to the frame and the spring pockets on the frame work great only real mod I had to do was take the spring holders on the axle off and mount my own so that I could run the GM coils which are 1. 5" smaller in diameter. I also cut the cross-member down and it fits the axle great now. So far it sits a little high yet so once everything is figured out I will cut the springs down an inch or 2 or 3. The GM coils are much stronger than the dodge springs or so they look!
As for the engine... I just got it mounted in on the weekend. Tight fit but it works, the hardest part of the hole conversion so far was figuring out the 6-speed and how to make it site and how low I could make it sit. I landed up making a crossmember out of 3" channel and some 6" flat stock. I made it hange down 2" below the frame and it looks like it is going to work great! Yesterday I just got working on the intercooler. I used a Duramax intercooler which has much more surface area than the dodge unit does. It was a tight fit but its going to work. It reaches out to the lights or a little past them so what I am doing there is putting a 1/4" spacer behind them which will bring the lights flush with the grill.
If you have any other questions let me know and I can probably help you out with them. I also have pics of how I did the mounts and the 4x4 conversion comming within the next week or so.
Good luck... Ryan