This has been built with a cross assembler, and the files 
have been tweaked slightly so that the listings will 
correspond well to the DECUS write-up, and so that 
directives not implemented in the cross-assembler are 
commented out.

"make" will built the binaries focal.bin and extend.bin.
These correspond to part 1 and part 2 of focal569.bin.
"make test" will confirm that the result matches the 
original images.

If you are using a simulator, you may wish to load/mount 
"part1.bin" and "part2.bin", rather than "focal569.bin", 
which is the concatenation of both.

I have not found source for the 2user overlay (mentioned
online but not in the write-up).

    Vince