What communication protocol do they use?
Ok, perhaps you should keep the ATMega8.
Well, the main reason for the 68008 was the simplified PCB layout. Only a half or quarter of data lines have to be routed.
The 68030 can also operate with only an 8 bit bus, so you can boot from a single 8 bit device but still have 16 and 32 bit devices as well.
Maybe PS/2 SIMMS instead of these old 30 pin SIMMS
Or even SDRAM, though that too is getting harder to find.
Lee.