crankshaft?

ok so i need a new crank for my pre-magnum 360. mancini is having a special on 4" stroke cast cranks to make a 408.it says balancing required,now can i use my 360 harmonic balancer and flexplate and torque conveter to balance this setup? or does the crank itself have to be balanced before it gets put in the block,i really like the idea of stroking this thing while i got it apart, this will be a street car so i wont be spinning it up past 6000,maybe a little more if i feel like having rice for dinner,just need some input.