When you figure in the cost of new mounts, flywheel, exhaust/intake dizzy, alternator, oil pan etc. the cost diff might not be so much. But if you are seriously trying to make 650+ HP from a BBO, there are no cheap routes. Why not build a <600 HP Olds and live happily ever after? Or put some squeeze to it with a turbo/blower. A true 700 horse motor can be a bit of a maintenance monster.