OK, I've got some more digging to do.

The three txt files are part of the Screen4 archive so are automatically in its directory.

The screen4.xml file in the Mach3 directory on my home desktop PC (installed but never run) where there is a functional copy of Screen4 consists of:

<profile><Locations><MachLocation>c:\mach3</MachLocation></Locations></profile>

so that is indeed only pointing to the absolute path of Mach3.exe (kind of pointless, it seems to me, since screen4.exe is specifically installed in the same directory of mach3.exe...)

OK, I just tried copying the whole installed-but-never-run Mach3 directory from my desktop to thumbdrive, ran screen4.exe and pointed it to the directory on my thumbdrive, exited, re-entered and loaded my screenset.  I'll just take whatever extra baggage is along for the ride...

Thanks for your replies, Dave and Gerry.

Randy