what might be of help is the series that appeared in Radio Electronics over 20 years ago which described the construction of a 68k based puter that could use actual IBM cards (my guess is though they had to be pretty dumb though). Generally cards are assigned the tasks of initializing themselves, so in my mind there doesn't seem to be any necessity of using 80x86 code. But I would have to imagine a great number of cards wouldn't cooperate nevertheless. A CGA card was supposed to work though. Note though that thee actual cpu was on the main board, IIRC.

Andrew Lynch wrote: Not ISA bus, but I built a homebrew 68020/68881 board for the Apple II back in 1986. It had an EPROM with boot code, and 32K of SRAM. It used two eight-bit parallel ports in each direction to communicate with the Apple, and allowed either processor to interrupt the other. Richard Ottosen helped me build and debug it, and Loren Blaney developed a version of the XPL0 compiler to produce native code for it. I no longer have the card, though I do still have the schematic so I occasionally get tempted to build S/N 2. Originally I wanted to design an upgraded version that could DMA into the Apple memory, for higher performance graphics. Eric