The custom PCBs should not be difficult to make, hopefully with a modern GAL. All that is needed is to force WE high during a CAS before RAS refresh cycle.

BTW, what is happening is that normally the larger SIMMs are put in bank A because of the way the Mac II memory controller is designed. Unfortunately the original Mac II ROM did not support anything bigger than 1MB SIMMs, the newer FDHD/IIx ROMs fix this. MODE32 supports larger SIMMs being put in bank B as a workaround by using the PMMU to remap it into contiguous memory.