You mentioned that the TRS-80(s) have hard disks. Perhaps the extra space taken by the hard disk bios is the culprit. Maybe a floppy-only machine (with floppy only bios) is the only way to compile it.
Will Grownups never understand anything by themselves and it is tiresome for children to be always and forever explaining things to them, Antoine de Saint-Exupery in The Little Prince
