If you are not planning on making over 600 at the crank then ditch the idea of a completely forged SB. I say this because the cast crank is plenty capable of handling that kind of HP as long as you dont try and shift at 7k rpms.
Simply get a quality set of rods, pistons, rings and bearings. Have the block machined and enjoy.
Exactly this. The cast cranks are not junk. They have their limits but for a mild build with 600-700 to the tire they will work. Just keep the rpms moderate and dont try and turn a cogged F1A with it and it will live.