I've broken my rule of not going over 45 bucks for any piece of retro hardware, and have purchased the only motherboard on the planet (yeah, sounds over-exaggerated, but for some reason it is just the sad truth) with the combination of: FCPGA-capable Socket 370, native 133FSB+AGP4X, AGP connector itself, microATX layout, multiple PCI slots and... PC/PCI pin header, be it damned. The QDI SynactiX 1 (seller photo attached).
It's for my slim-desktop Pentium III project, previously abandoned due to its <100% DOS compatibility when paired with my favorite soundcard - the ESS Solo-1 PCI (probably the only one out there that is capable of completely replacing an SBPro ISA card in terms of compatibility, but it requires a pre-ICH Intel chipset or a VIA one if no PC/PCI is available in order to do that).
I'll probably be bragging a lot in the future once it is received and the project assembled, but maybe not, we'll see 😁