Unfortunately, I can't get MS-DOS 2.0 to run in DOSBOX ("Invalid COMMAND.COM") and running MASM.EXE directly gives me some really interesting errors (looks like it's reading uninitialized memory).
I think you're on to something here, though!
Good job! I'm going to throw some cycles at this, this holiday weekend.
Also, as written in the blog post, the .ASM files are not the original sources, more a temporary expansion of these for the given target. Looking at their binary form, all .ASM files end with zero characters instead of, for example, 0x1a with which .H files end. It can be that some tools (different than those originally used) have problems with the zeroes at the end?
That's a good observation. I tried stripping zeroes, but unfortunately it's the same error message.