Ok, I built the floppy image now. dd'ed it on a floppy and powered my IBM PS/1 up. Despite some nasty sounds of the HDD bearings that went away after 30 seconds, the floppy does not boot on this machine. Just a black screen. 386SX-25 2MB RAM. Maybe 2MB RAM too less, but I thought at least something will happen. :-)
Even on 2MB, you should be able to at least see GRUB, which would tell you that it can't load the kernel. Does it go blank before that? This could mean an issue with either GRUB or the floppy.
In case you have DOS installed on the hard drive, you can also use GRUB4DOS [1] - just put gentleos.elf on C:\, run grub.exe, then `kernel /gentleos.elf`. You may first need to comment out any upper memory managers from config.sys. A bit of an academic exercise since the kernel still won't fit into memory.
Btw. feel free to reach out to me on my profile email. I'll be busy with work for the rest of the week, but later I may look for some workarounds to get it running on 2 megs.
For PS/1 you'll need the 16-bit version from https://github.com/luke8086/gentleos. A floppy image is provided in releases. Note you only need to copy the first 64KB, the rest is just padding for emulators.
The data bus was only 16 bits wide, but that doesn't really have much impact on OS compatibility; it just means that transferring a 32-bit value to or from memory takes two bus clock cycles instead of one. The address bus is only 24 bits wide, but that only affects physical memory address space; it still uses 32-bit pointers and a 32-bit virtual address space.