Try it now!!
Disregard the red words, I have since figured out that these holes are the exhaust ports for the EGR. They need to be plugged on a boat.
This is the back of the heads on a fuel injected 351W in a ski boat. Its the 310HP marine engine with the GT40 intakes. I'm not sure if they are GT40 heads you guys are referring to, but I cant imagine that changing the 2 intakes to the GT40 would give a 100 HP increase over stock...so I'm assuming the heads are the GT40 as well.