Generation IV Internal Engine - LS3 head rear coolant passage...

I got a set of LS3 heads recently. It looks like the rear coolant passage on each head is plugged with something. I can't tell if something was broken off in each or if they are supposed to be blocked off or not. Do LS3's use the little screw on plugs on the back of each head like the later LS1 engines?

The heads are plugged like that from the factory. That is normal.

If you are running FI, N2O or high compression, I recommend drilling and tapping those holes for AN fittings and running coolant bleed lines to the front...

Shane