You can add the data to the actual mvpart as custom data and then read the data using property sets. Or you can just add the data via a property set and attach to the mvpart. I would suggest adding the data to the actual mvpart as individual parts can have a different amount nuts bolts etc. The property set would automatically show up on the property palette under the style based property sets.
Here is an article that might be of use to you as well as a document from a previous Autodesk University class:
The AU document is kind of old but the concepts are still the same.