It's not going to be as easy as just getting components without the custom programmed ROMS it wont work. There is a simpler version of the expander listed in the A1000 Service Manual.
I talked to someone who used to be involved with bill's board. He
pointed me to this:
http://olson-ndt.com/AMIGA/BusExpander/Looks like there's schematics, information about trace errors on the
board, and some experimental equations for the PALs, but apparently
the originals are lost.
brian