The lower SIMM socket? That could be trouble. My limited knowledge of the A4000 tells me that's the CHIP socket. Or do you mean the one closest to the edge of the board? I think that's a FAST socket.
If it is in fact a FAST socket, I *think* you could use 8MB SIMMs in sockets 2 and 4. Don't know for certain, though.
Hope this helps.
