What is the best way to find the delta between 2 versions of a process model?...

One idea is, you can verify the process model's XML file for different versions using diff tools. You can get to the xml versions of your model by browsing to your Appian installation directory - file store location (by default _admin directory) and then going to the models folder.
Other idea could be, visually check the versions of the process model.

One idea is, you can verify the process model's XML file for different versions using diff tools. You can get to the xml versions of your model by browsing to your Appian installation directory - file store location (by default _admin directory) and then going to the models folder.
Other idea could be, visually check the versions of the process model.