How to Perform a Maturity Assesment

I've just started a new role at a company who hired me to bring in a bunch of new and exciting technology (IaC, containers, CI/CD). The issue is that they need to make a lot of changes to be able to support all this new tech (To give you an idea, they are still using subversion with one branch for multiple applications).

I was wondering if the great hive mind of HN is aware of any existing maturity assessments, lists of questions or anything I can use to support my case that we need to make some fundamental changes to process (and probably org structure as well) before we can start implementing all the shiny new stuff.