It will contradict what some people say, but all I can do is share my experiences.

I built a 408 using an eagle 4" cast crank, eagle H beams and SRP forged slugs. It was supplied as an internally balanced rotating assembly. When I received it I noticed it only needed minor drilling to internally balance, no mallory at all. It seemed odd to me and I contacted the shop and there is apparently some misinformation with eagle's specs on their cranks.

I put a neutral balance SFI damper on front and a neutral flexplate/converter combo and it ran great. Ran 11.90s in my F.A.S.T. Duster while the big motor was being built.