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

I'll be the one to state it.
This is a terrible idea. You're installing an engine in a car that already has a 55/45 front weight bias and literally doubling the weight of the engine.
The frame rails and structure were designed for the slant six or LA series engines that weighed 600 lbs or less and made less than 350 lb ft or torque. No current front suspension will be enough. The factory K member is far more robust than any aftermarket setup and even those are nowhere near as durable as you will need. To do this, you will need extensive structural reinforcements which may far exceed your skill level and budget.
I appreciate doing something different but in this case, Why? What possible gains do you expect that you can't get with a turbo V8 setup?
Oh, I agree this is a terrible idea, and I'm well aware that it is going to be incredibly front heavy, and it will indeed need a lot of reinforcement. I'm tired of seeing cookie cutter builds, and no one's swapped a 5.9 Cummins into a Duster....for good reason, but still.