Maybe it be an Acer.
I don't think a 586 is a good idea if you got a 486 lying around say dx33 this would be stable enough to read its oem signon (the post screen string).
I like the button cell on the dallas RTC I don't like the system board ram looks small what was cool was ability to replace across brands with lower latency chips (for full 640k).
A limited info from google revealed Wims Bios forum has a database to identify oem strings. The string has manufacturer, chipset etc.
If no luck then it will show what cpu it is configurated for and perhaps that should be the safe target of operation.
Information is scarce because back in them days there was no pdf and most info was shipped with the unit on paper. websites were very small only advertisements no self support sections with bios, manuals.
I got this far but it be Russian https://groups.google.com/g/fido7.su.hardw.ch … U6O48oXAJ?hl=en

Found that same too but this seems better:
http://www.win3x.org/uh19/public/motherboard/ … f6310945520.pdf

It's very blurry but jumpers makes some sense. Mobo is not the same still.

Bios ID says 8021 so it's an Acer.

Up...

Seems like there simply isn't manual for this mobo anywhere in digital format.

And after all these years, here it is: https://theretroweb.com/motherboards/s/mg-pci-isa-ud-486-grn

I just don't have that mobo anymore...