In this photo, you can see that, different from an iron big-block, the top of the cylinder bank has screw-in core plugs. There are four such plugs: two per bank. Also, note the cast-in pedestal, one of two in the lifter valley. The roller lifter retainer, or "spider" as it's also called, bolts to these bosses. They're for use with the production-style Gen VI "finger-style" lifter desgin.