Inter-Project Billing Extension

I am working on an inter-project billing solution to pass costs between 2 ledgers. Standard functionality provides for selecting one task on the receiver project, and setting a default expenditure type for all items. I worked on implementing this at another company, and we used the extensions to break out the transaction detail and pass it to the receiver entity as it is captured in the provider entity (as shown below).

Provider Project A invoices:

Task 1 Labor expenditure items

Task 2 Non-Labor expenditure items

Receiver Project B receives:

Task 1 Labor expenditure items

Task 2 labor expenditure items

Based on the documentation it looks like there are 2 extensions in play: the Internal Payables Invoice Attributes Override Extension and the Provider and Receiver Organizations Override Extension. Are there any other extensions that come into play?