27C400 are 256Kb x 16 bit, so no, you can't for this use.
you need 512 x 16. maybe the 27C800, but wait for others confirmation as i'm not really sure 
edit : i checked pinout, you can go for 27C800.
WRONG! The A4000 has 2 ROM sockets so 256KB x 16 x 2 = 1MB! :rtfm:
