Hi, Well having the 5th and 8th cyl.s with coolant it is highly possible that it is the intake since the coolant passageways in the head mate with the intake on the ends. The question though is do you have coolant in 1 and 4 since if the intake gaskets are the wrong ones coolant should be leaking on both sides. It is more likely when it is the Intake gasket, to get antifreeze in the crankcase not a cylinder. The intake has to come off anyway to get to the heads, so I would remove the intake and check the gasket to see if it mated correctly or the right one. If You don't see anything obvious there, check the head gasket by closing the valves in 5 or 8 pressurize the cylinder and check for bubbles or coolant rising in the radiator. Actually if you wanted You could do this procedure first, to see if it is the head gasket. I have found that when installing aftermarket heads always check the gasket to make sure it will seal all passageways. Some are cut different.
