Software Integration in V-Model, developed in SAFe

Hi Everyone, really need your experience on this 🙂

Institution A is developing a software using the SAFe methodology (Agile) for institution B.

Institution B only works in v-model and will be integrating the software in v-model.

Hence, institution B is missing their expected documentation in v-model…such as the management rules of th software developed.

They don't want to end up with user stories.

What is the best approach regarding the documentation of requirements/functional SPEC?

Many Thanks!