Once you've got that working, try installing a 2.11BSD distribution. It's well-documented and came after a lot of the churn in early Unix. After that, I've had great fun playing with RT-11, to the point that I've actually written some small apps on it.
If you want to play around with RT-11 again, I made a small PDP-11/03 emulator + VT240 terminal emulator running in the browser. It's still incomplete, but you can play around with it here: https://lsi-11.unknown-tech.eu/ (source code: https://github.com/unknown-technologies/weblsi-11)
The PDP-11/03 emulator itself is good enough that it can run the RT-11 installer to create the disk image you see in the browser version. The VT240 emulator is good enough that the standalone Linux version can be used as terminal emulator for daily work. Once I have time, I plan to make a proper blog post describing how it all works / what the challenges were and post it as Show HN eventually.