Data in Navigocorpus provide information on the quantity of goods composing cargoes. This information is expressed in a extremely high variety of measures. In collaboration with the Sound Toll Online project and with a research team on balances of trade coordinated by Charles Loïc and Guillaume Daudain, Werner Scheltjens is working at a database which allow a conversion of the different units of measures into a metric system by taking into account the nature of the good and the place in which the unit of measure was used.
My attention was drawn to your site by a friend who read you recent article in the International Journal of Maritime History. Some years ago, I put together detailed work on pre-decimal measures, running to several hundred pages. The majority of data is obviously English-based, but is mostly derived from primary sources, such as Acts of Parliament.
This work has been sitting gathering dust for over a decade but might save you a lot of duplicated effort. It might just be worth exploring possibilities.