Hi Bill
Here is a whacky idea: would it be possible to use a chip like a PIC16F13145 with CLCs (configurable logic cells) for the logic and built in Flash to store the SP0256 ROM data?
Put the logic in the CLCs and store the data in the Flash. Then it would be only a single 20 pin DIP part for both logic and ROM data. Burn the PIC16F in your programmer in one operation.