Use item on the Billing process

We have a requirement to use Inventory Item for the billing process initiated from the PPM Contracts. We are using a manual event-based billing option. On the External contract, we can capture item information on the billing event level but for the Internal contract (interProject) we don't have that option to provide item information.

If anyone has come across a similar requirement request you to suggest possible solutions for the below statements.

1. How to capture Item information on the billing process for both external and internal Contract/Billing events?
2. Is there a way to establish some linkage based on the item used on the contract/billing event back to the Item master?