I have a few PowerPC parts but yours does not resemble anything I have from memory. For one the board is very narrow compared to any of mine. Will look them over when I can, may be a day or two.

Bull computers?
https://www.asap-ittechnology.com/quote/bull/01w3230f/
possibly:
https://www.zdnet.com/article/bull-motorola-f … owerpc-nt-exit/
http://www.feb-patrimoine.com/english/power_pc_products.htm

Could be, for sure. But I found this ended eBay listing of a PowerStack and it seems like it has exactly the same board inside:
https://www.ebay.com/itm/Motorola-PowerStack- … C-/333612892566

You were right, this comes from a Bull machine!

I received the riser today and it just works fine! I had to try a few graphics cards, but I found one that gives an output. An STB Horizon+ PCI.

I found this ( https://web-docs.gsi.de/~kraemer/COLLECTION/M … ROLA/mpsii.html ) on the Internet. This explains why the board looks the same like in a PowerStack II. There seems to have been a Bull Estrella 300, a machine that I cannot find anything about on the internet. I guess if this custom Bull BIOS does not work out for me, I can just flash the one for the PowerStack.

Of course the Timekeeper RAM is dead and for some reason they had to use one that is soldered onto the board... I really hate these Sun NVRAMs, but at least you can swap them out easily. It is actually better than I thought. This module has a so-called "SNAPHAT" battery on top of it. Just ordered a new one.

There seems to have been a Bull Estrella 300

Nope that was IBM, not Bull/CMB. There are exactly 3 scientific articles that mention it, like this one:
https://www.researchgate.net/figure/Compariso … le_fig5_2396730
I'll dig a bit more to see if I can find an actual model name.

The funny thing is only servers are mentioned here, no workstations/desktops:
https://en.wikipedia.org/wiki/Groupe_Bull#Hardware

Good on you getting it to boot, please see if you somehow can make a backup of the bios, it might help others in the future.

I just guess that this Wikipedia list is quite incomplete. It probably is not that easy to find out nowadays what their total lineup was. While I have no idea about Bull, I might imagine that they sold a lot of products into non-English speaking countries.

I was able to backup the Bull branded OpenFirmware, I posted it (bull_of.7z) here:
Re: Windows NT on Motorola Powerstack II

So, as I luckily got it all working recently, I want to put this board in a case. I am not really experienced with retro hardware, so I might imagine that some of you here have a better idea about what to look for here 😀

Basically, I just want a (ideally cheap) functional case, it does not have to be super pretty or historically accurate. Actually, I would prefer some new case that I just can order online, as I am not really a fan of yellowish plastic that tends to break apart...

Thanks for any help and hints here! (It also would be quite helpful to know if this board matches any standard, dimension-wise!)

The problem, of course, is finding a case that fits. Considering most PC LPX cases (which this resembles most) have some features that likely won't make it fit, perhaps consider making your own custom enclosure based on a blank lab electronics casing? You just need to find one large enough to host the board and make all holes by hand...

Yes, I guess I will have to build something myself. I think I will try to use a used ATX tower that I have here. I think as long as I am able to put the standoffs where they are supposed to be, I should be fine. Probably I will have to build some form of mounting for the single PCI card that I plan to install. Maybe I can also 2D print something.