A couple years ago I looked around the net for some info on interfacing the 680x0 to the PCI bus. I did find an application note for a circut that used 2 chips. One was the companiy's product, the other a generic PLD with some glue logic defined into it. Even had the equations for the PLD in the note. My notion was to hang this off the back of the GVP card in my 2000.
Doing the ISA bus would be easier. There was a card on the market that did it... I think they just mapped the ISA expansion space into part of the Zorro II memory space.