Hasn't happened too me but, i run belt drive pumps and conventional covers except on the blower motor, and it doesn't have a balancer, only a blower drive hub and a timing ring. You maybe could fix it by grinding off the fins and adding the thinnest spacer that you can use behind the balancer.
I'm not familar with a 6 cyl. crank, but if they are 1 1/4" dia. like the small blk chevy you can get spacers any length from mscdirect.com used on a horozinal milling machine arbor and they will already have a keyway cut in them or if you have access to a lathe you could make one. I wouldn't want to hang the balancer out any more than necessary to clear the cover.
JMO
Zip.