You could manage an 8-byte snooping window with a handful of logic chips, though as has been suggested an Arduino-based snooper would probably be both easier and more scalable.
The simplest thing would be to only snoop the bus writes, in which case each of the eight bytes displayed wouldn't update until written to after boot or after moving the window.
You could add some additional LEDs though to mark which of your bytes are currently valid.
I find the logic chip approach to be a fun exercise though, so here's a few that you could use for this:
- 74x521 Identity comparator
Using a couple of these you'd match on all but the three lowest bits of the address bus to generate a chip-select for your register. - 74x138 Decoder
This is what you'd use for the lowest three bits of the address bus to select which of your 8 bytes is being written to. - 74x573 8-bit Latch
Eight of these will store the bits that your LEDs show. - 74x259 Addressable 8-bit Latch
If you do use an additional LED per byte to indicate the validity of each byte, this would be convenient for storing that flag. - DIP Switches
Not a chip, but you'd need some way to specify the higher address bits that position your viewing window. Though you could also use another 74x573 and control it from your computer directly.
As for connecting the LEDs, you *could* wire them up to the outputs of the 573's but it would be a LOT of wires/traces. Multiplexing the LED matrix would be a good idea here. You'd use another 138 decoder, a counter (74x161 or 74x163 for instance), a multiplexing switch like a CD4051, and some clock source like a 555 timer circuit to rapidly cycle which row is being lit.
If you wanted to show more than 8 bytes you could connect fewer of the address bus bits to the identity comparator and use bigger decoders, more 573's. That gets pretty expensive and unwieldy fast though.