Crate Killer Heads
I think the name reflects that we use these on our crate killer engines.  These are stock GM Castings that we do all of our work to.  This includes installing screw in studs and guideplates, CNC Porting, Valve Job, & Milling.  For cast iron heads, these are the lightest ones available.  I really like these on smaller cubic inch engines with flattop pistons & flat tappet camshafts.