my cast crank was internaly balanced, it didn´t need heavy metal because of my light weight components. it lasted 2 years of racing, i use to take this up to 7200 rpm but I beleive my trans brake snaped the crank into two pieces between number 7 and 8 cylinders. The motor was still runing, no damage to the block. The two rods kept the crank together. To rebuild my motor I used the same block, two new rods and a scat forged crank.
At the time I built the motor, I didn´t have the money to go forged, so I build my motor with what I could aford, not expecting it to last for a long time however I enjoyed my car for 2 years