Use Receivables Transaction Type to Derive Account in SLA?

Summary:

We just set up project billing and are trying to create SLA rules for external revenue. Is there a way to create a mapping set based on the Receivables Transaction Type we're using?

Content (please ensure you mask any confidential information):

We created a new transaction type for project billing/contracts under Setup & Maintenance -> Project Billing Base -> Manage Transaction Types. However, if I try to use transaction type from Receivables, we don't see any of the ones we've created. Is there another Transaction Type lookup or is it not possible to use an input from Receivables in Project SLAs?