to answer my own question: looking at the 2445 service manual (and the 2445A service manual that I have a physical copy of) it looks like the low 2k of memory is external RAM with no special function, so unless there are other bus masters in the system (e.g. DMA controllers) it's unlikely that anything other than the CPU cares what is in that memory space. This 2k contains the 128 bytes that are on-board in the MC68A02, so it would be fine if either then on-board memory serviced those reads/writes, or if the those reads/writes went to the external memory.
More importantly, however, is the RE pin (pin #36) which is the "RAM ENABLE" pin on the MC68A02. The on-board RAM is disabled when the RE pin is in the TTL low state, and on the MC68A08 the RE pin MUST be tied low, so if you put an MC68A02 in place of an MC68A08 it should act just like an MC68A08 (at least, that's how I read the data sheet).
I'd say it's worth getting an MC68A02 and putting it in; it can't work LESS than the current chip.
-- Jeff Dutky
