Hi,
If the Material Consumption plus the Inventory is also to be tracked for the New Production Line, would suggest to have a Project System in place. Create a Project for the New Production Line, WBS Element can be created on which the Purchase Order / GR can be made and could be settled to a Fixed Asset.
If not Project System, then an Internal Order could be created for all the expenses/income for New Production Line. Creating an Internal Order would not have the stock information. Later Order could be settled to a Fixed Asset. Also would suggest to have a Line Item apportion for better picture.
BR, Jaymin R. Bhatt