Ok… I fixed the line weight display in piece and layout mode… changes are pushed and waiting for PR to be merged.
Indeed it was just a matter of converting the mm default prefs to pixels. Also note I also fixed another existing issue with the internal paths, where the lines were zooming, instead of maintaining the same line weight. BTW… in case anyone is wondering I refer to the pen width as line weight VS line width - a line weight maintains the same width regardless of the zoom factor where a line width changes with the zoom factor.
Also of note… I did make sure that the line weights default to 1.2mm to be consistent with the existing line weight, although I thought they were 1.0mm. IMO the default should be 1.0mm as it’s an ISO 128 standard width. BTW - I also fixed the max num of drop items to show all - no scroll:

Also in case anyone is wondering… ISO 128 defines widths as well as colors. For example: the US National CAD Standard adopted ISO 128:

And for those familiar with drafting pens from the likes of Rapidograph, the width is color coded as per ISO 128:
The reason I mention this is in some manner I would like to add an option to semantically tie the ISO line weights & colors together… where if you select a line width it automatically sets the color or vice versa.