Heterogenous lists in Keystone 6

I have a few "XXXScreen" entities in my schema which represent configurable screens in an app. I want the CMS editor to be able to selection instances of these screens (created in keystone) and arrange them as a list under a "Study" entity. I'm wondering if there is a way to do this with references or if not, some other way...?

I was considering something with Slate document blocks but I'm not sure it supports changing the ordering...

Thx!