Y Block cylinder heads

Sorry if this is the dumb question of the month but could I blast my cylinder heads myself with my blaster. I have a medium grit wallnut shell that I am using for a media and am unsure if it would harm the head. The heads are 1960 292 truck heads.

 

no harm from that blast on

 

sweet

 

I hardly think walnut shells would harm cast iron, its pretty tough.