how much time do you have ? how many big blocks have you built ? i have built over 100 of them from 369 to 600+so here is big block 101 . steel cranks ring like a bell .thats harmonics bad if not dampen .look at it is way less amplitude of harmonics is a good thing cast cranks hase less harmonices it will not ring like steel you say no big deal ?? busted valve springs some times is harmonices . I will not use gear drives. this sends harmonics thur crank to cam thur lifters to springs .you said stock engine have cast cranks .yes that right . but do they make 600 hp ?? cast cranks do not like to be twisted ? you said crank are made to be twisted that s rigth but are they running up 6800 rpm and 600hp? they are things to do to keep the cast crank alive like 4-7swap this is good for 20 hp helps crankshaft deflections =twisting .the 5 -7 firing order it is hard on the cranks .steel @cast so hey fix it 4-7 swap and it good for 20 hp ?and it cut s down on crank deflection =twisting all thing s I think of when i bulid a 600hp big block and more.I do not give bad info. all my info can be back up.if you dont think it right. i will keep it to my self .and you can learn the hard way. they are people who give bad info i am not one i have built big blocks for over 20 years .you said you never heard of this? good engine builder dont tell you evey thing .