I can't tell you exactly how much needs to be removed from the counterweights on a RB crank, sorry
I think you can chamfer the #5&6 counterweight on the outer edge that faces the #4 main webbing a little bit, maybe a 1/4 inch to make it clear the low deck block main webbing.
A lot of the better machine shops down here in the U.S. cut, trim in a lathe, the outer counterweight ends off to help balance them better with the longer rods so they don' have to drill holes or add heavy metal to get them to balance better