DOSBox does a pretty good job at emulating DOS. If all else had failed, an option would otherwise have been to use QEMU, create a tiny virtual machine with an installation of MS-DOS (can be found very easily), and run it from there. Don't know how well QEMU works on POWER9 though, if at all.
my boss and I spent ~50K euro on Power9 and Ampere ARM/64 servers; programs like Qemu have high priority, so, if it has some troubles, we are the first persons who have a serious interest to fix it.
I didn't emerge DosBOS from the portage but rather from my Overlay, that because DosBOS is more a sub-project, an attempt to embed commercial DOS compilers that are not linked to conIO into a CLI-only sandbox, so you can launch them on bash, as they don't need any SDL or X11 interaction, they are just files in, files out.
Nice! And very useful to support the type of customers who still use DSP for older radar systems. All things that only DOS compilers have.
"Draft.exe" (OrCAD Schematic for DOS) massively uses not only the conIO (text console IO) but also a graphic driver for VGA cards, so ... it was also a good occasion to test my patches, specifically if the "dos sys call probing" was able to correctly catch, by analyzing the file function calls in the .exe files, the kind of requested application interface.
I found a small bug. So, that was twice helpful!