You can use MSI + Product Module to make a cradle-to-grave carbon footprint. For calculating Scope 3 GHG emissions associated with Category 1 Purchased Goods and Services you would take MSI data + BOM and Finished Goods Manufacturing from the PM.
If you want to use FEM data, you could use MSI data for measuring BOM-impacts, and use FEM tier 1 data for calculating impacts associated with product assembly. The impacts that are not covered in this scenario are impacts from transportation from tier 2 to tier 1, and the loss rate of material usage at tier 1 level.
Disaggregating MSI process data is not possible (you can only see process impacts in the tool but you cannot download these to Excel) and for that reason, our tools do not support using FEM data for tier 2 in combination with MSI data.
A useful resource regarding calculating Scope 3 emissions using different methodologies from UNFCCC can be downloaded here under Working Group Drafts.