^^ what he said. 3 front are all coolant, I use the one you have marked as heater and capped the other 2. Egr is egr, the one behind the carb is manifold vacuum.
Ok. thanks, axis. Good to know what the carb one is.
The intake specs said its not x-over plumped for EGR. "To hook up EGR with this intake, following parts are required:10220275 EGR pipe, 12552329 fitting, vortec exhaust manifold # 12557828, 12557828DT (tapped for O2 sensor) or ED1476 weld-on fitting kit for use with headers."
But you are running yours with no issues. So will follow suit.