Dragula, I had, sold it, a 526 CI motor(4380borex4.375 stroke) in a stock 440 block with ductile iron main caps make over 845 HP on race gas. It was dyno tuned and I ended up melting three pistons on the dyno due to a loose power valve block off plug in the rear carb., I kept leaning all eight barrels down and the motor kept gaining power until it melted those pistonsI didn't pay enough attention to the 8 EGT and AFR from one side of the motor to the other The new owner has not raced that motor yet, he is building a new car, it isn't done yet, he went through a divorce and so on
My message is the larger motor will make more power and strain on the main webbing, buy a good block or keep the power down below 700 HP and shift it before 7500 RPM I've seen several stock blocks, 426 M.W. and 440, break the main webs at or close to 650 HP As Monte said some get away with stock blocks and others have wreck and injured themselves do to block failures while racing, don't take a chance