Q&A

Do a compression test, if you have good compression check closer for the intake.
front or back corners are where the water jackets are, If the gasket has internal water leak it will run into the valley and out the oil pan.

doing a leak down test would give you your answer. air is applied into the cylinder and if it pushes coolant out the radiator, then you have a head gasket issue.
take your time
it is most likely the intake as a head gasket would produce a check engine light and severe driveability issues.

Roy

If water flows thru that easy, I think it would be a craked head or block. Gasket leaks usely are very slow and require cylinder/engine pressure. Pull heads and this will let you visually inspect both intake and head gasket problems. I'm really thinking cracked head or cylinder. Start by pulling plugs and see if one cylinder is filling w/water quickly and running out plug hole. You didn't say if water was getting in oil. I'm responding thinking it's not.