This is an incredible find. It would be amazingly cool if we could create an emulated environment for compiling and running Unix v4 from these sources.
For me, it's a chance to experience what it was like to use and develop software on these systems back in the day. For example, lately I've been writing some small apps and adding new kernel features to a variant of V6 Unix running on my PDP-11/05. It's humbling to see what it really took to be productive on these systems.