Is there a difference between the 1.7 and 2.0 d-Jet systems, or are they interchangeable?

They are similar but have specific component differences.
It depends on what your notion of interchangeable is.

Same parts in general, but set up differently. Injectors have a different flow rate, MPS is calibrated differently, ECU is set up slightly differently, some wires are longer or shorter, etc.

--DD

Thanks!!