I didn't think I had any 8086 software tools on my PC but I was pleasantly surprised to find that I did.

For disassembly:

objdump -D -b binary -m i8086 SV25mon.BIN

Add the option --no-show-raw-insn to omit the hex bytes.

 For assembly:

as86 SV25_assembly.txt

 This will be handy for developing code for my other 8086-based boards.

as86 has a syntax that is significantly different from the online assemblers and disassemblers.

nasm is much more consistent, so I have moved to using that.

ndisasm generates code in the right syntax for nasm, so I took the disassembly and re-worked it.

Checking the output is difficult, because the 8086 has multiple opcodes for doing the same operation.
nasm generates codes that differ from the original ROM.  There are too many to deal with in the time I have, so I am shelving it for now.