The daves garage youtube has an episode where he documents the pitfalls of compiling 2bsd for a PDP-11/83. https://www.youtube.com/watch?v=IBFeM-sa2YY basically it is an art on a memory constrained system.
What I found entertaining was when he was explaining how to compile the kernel, I went Oh! that's where openbsd gets it from. it is still a very similar process.
On openbsd it's
cd /sys/arch/$(machine)/conf
cp GENERIC CUSTOM
vi CUSTOM # make your changes
config CUSTOM
cd ../compile/CUSTOM
make
I have never done it for 2bsd but according to http://www.vaxman.de/publications/bsd211_inst.pdf
cd /usr/src/sys/conf
cp GENERIC CUSTOM
vi CUSTOM
./config CUSTOM
cd /sys/CUSTOM
make
What’s the process look like?