Somewhere, I have a printout of the (quite slim in terms of page-count) Oberon manual --- turns out there is a Pi build:
http://pascal.hansotten.com/niklaus-wirth/project-oberon/obe...
will definitely have to experiment with that.
EDIT: but it's apparently an emulated version?
Perhaps:
https://github.com/MGreim/ultiboberon
is better?
Or ditch DOS and embrace Wirth's Oberon (the OS and language).
There is a one-floppy build.