What's the goal?
Nothing made from a B block will inherit the huge volume of data, reccos, tune-up specs that a 426 RB will (not re-inventing the wheel). Scaling down the existing dimensions (especially de-stroking) has disappointed many, many people going back over 80 years, including Chrysler and Harley-Davidson.
Among those that will need A > B comparison, if not actual tweaking, are:
different manifold characteristics, both plenum volume and runner length
rod ratio
intake:exhaust port flow bias
spark advance
cam LSA and install point
crankcase pumping
piston dome shape w/r/t overlap breathing and spark flame front