Thanks for confirming H3NRY. Not sure I understand the +5V resistor, where is it? It appears the W1 jumpers to nothing, or a ground layer to which numerous things attach all over the board.

Another thought occurred to me. The Mac Plus has the same RAM decoding multiplexer chips right? Would there be a way to configure the Plus in the minimum 512K SIMM configuration, then disable a multiplexer chip to recognize less of it, say even down to 128K? (I mean why have a 4-in-1 when I can have a 5-in-1?)

Is there a Mac Plus logic board schematic someplace?