Monte and Al are spot on IMHO, and much more experienced with combos than me for sure. Looking at my latest combo, I chose a 4.15 stroke/4.500 bore over a 4.50 stroke 4.500 bore because I didn't feel I had the head flow to support a 572. I have about 375 cfm head flow at net valve lift in my motor, and it is all done making power at 6900 to 7000 rpm. A 604 motor would need 428 cfm of head flow to equal what I have, and still is hampered by the same size bore as I have, and hoping to push more air through it.
IMHO I would go 4.25 stroke 4.500 bore for 540 cubes. It is a great combo, and a local Supergas racer ran this combo in a low deck KB block with B1Mc heads twenty years ago, and was going as fast as anyone I have heard of since with those heads.