Deleting Internal Requisitions is it possible?

We have millions of iinternal requisition lines that I would like to delete from the system.  They cannot purge as they are source type Inventory and the normal purge process will not touch them.

All of the inventory transactions and the Internal orders have been purged for the dates in the delete range.  All of the requisition lines have been fulfilled or cancelled.

Do I need to delete more than the requisition distributions, requisition lines?  I will finally close the headers after the lines have been removed so that they will purge out.