How to model a single Supply plan run across two Oracle Fusion Cloud Instances

Summary:

Currently we have two separate Oracle fusion Instances operating with different Supply Chain Plans.

in short term we are looking to consolidate these two Supply Plans as a single plan run in one of the Fusion Instance. How can this be achieved? Do we need to model one of the Instance as EXT Instance even though these are both latest Oracle Fusion Instances ? Are there any other options? In short term we are looking to consolidate the Financial Track and Procurement Track to single fusion Instance, however we still need to keep the inventory and Manufacturing in two instances.