It's odd that even for our little 4-bit part, there are few options listed. It looks like for it to handle the old Altera, Xilinx CPLD and serial proms, I would need to up my game. I still have some old project that use these parts and am thinking that if I am going to spend the money, I want to support all of my past projects.
Thinking of the 4-bit part, I should have added the W3 jumper. Remember when I talked about U24 having the A13 pin routed to possibly support a larger part rather than a NC? Well, as we can see, this jumper was added to support that feature. The memory map is still linear. U24 still acts as the boot ROM. Everything else is just moved up. It's good when things make sense.
I wonder if any of their meters ever took advantage of this larger part.
U24 0x0000-0x3FFF PROM, 27128, 16K 3FFF
U23 0x4000-0x5FFF PROM, 2764, 8K 1FFF
U22 0x6000-0x67FF RAM, D4016C-2, 2K, 7FF
U24 0x6800-0x6FFF E^2, X2804AP, 2K, 7FF