Wanted to share this for others to build on.
This is a Dynamo script to Renumber Fabrication ductwork using a SPLINE to define the order to Renumber.
Image 2 - Draw a SPLINE overtop fittings to define numbering order...SPLINE must touch each fitting.
Image 1 - Pick Select, select the SPLINE, click Run
*Uses the Item Number field so it will export with .maj
*Does not take into account like items