Greg,
No, I think you have the pins wrong when converting from a AT28C64.
Pin 24 on the 2732 (VCC) is pin 26 on the AT28C64B. So when the 4K rom is selected on the motherboard you need to supply pin 28 on the AT28C64B with what the motherboard is supplying to what it thinks is pin 24 on a 2732. This is pin 26 on the AT28C64B. Since pin 26 is not connected to anything in the chip you are just running from the location of pin 24 of the 2732 to the real VCC of the AT28C64B.
Get it? It works fine and is what the converters do with a conversion board.
Gary