Balancing a Scat cast crank

It depends on the rods and pistons you are using. The SCAT cranks are designed to internal balance with a bobweight below a certain limit. If your bobweight (which depends mostly on the piston and rod weights) is too high, then it won't balance internally without mallory or external weights. In fact, the catalog states for this crankshaft "Internal Balance, May Require Mallory". See here , on page 18 at the bottom:
http://www.scatcrankshafts.com/wp-content/uploads/SCAT_Crankshafts_Catalog_Nov2016.pdf

The SCAT rods are fairly light but the Icon forged pistons are not as light as you may need. Which rod and piston PN's do you have? (I am guessing PN 2-ICR6123-2124 for the rods but there are 6-8 PN sof the Icon pistons.

Also, look at any tech sheets sent with the crank? Does it specify anything about bobweights?