Rogers, you will end up with a 427, which has the same bore as a 454 and the same stroke as a 396. If you don't have a 454 balancer crank and flywheel I can see why you want to stay internally balanced but otherwise it makes little difference for all but super high rpm stuff. I spin a blown 540 to 7400 with external balance and have seen no issues whatsoever after 2 1/2 years.
DJ