I'm Cummins swapping a '74 Duster, thought I'd share the progress.

I agree with Kern Dog that this idea is ill advised. Just because something can techniclly be done does not mean it should be done. Putting a Cummins into a D150 or something would be a natural swap but shoehorning one into a smaller passenger car makes little to no sense. It's not a passenger car engine, it's a truck engine made to haul heavy loads. You're also going to have a rev limit of less than 4,000 rpm which does not sound fun.

But besides the chassis stuff, how are you going to cool it? Those things run pretty hot (215-220) and could potentially melt stuff under the hood without proper ventilation. You'll also have to science out your fuel system pretty thoroughly to run diesel. And what trans do you plan to use? Whatever it is won't fit without cutting apart all kinds of structural pieces of the chassis. So not only are you adding a bunch of weight up front but weakening whatever is behind it.

I'd think this through a little more before you start cutting stuff making the car un-sellable should you decide to abandon the project before its finished.