Check the DevNotes, if they don't give you the ROM pinouts outright, you can pretty much determine which address/data lines were left unimplemented from the full memory bus from the info in the memory map diagrams and the Block diagrams. IIRC, it's just a subset of the Full RAM bus . . . say 24 bit for a 32 bit system.
I'll take a peek at "Designing Cards & Drivers for the Macinto . . ./whatever" to see if the pinouts are listed for the ROM Slots.