looking at the spark plug, it's kinda clean so it's probably coming from other than the intake runners.
i mean if you were trying to ignite an oily mix the plugs would tell you about it. And this stuff is pouring out the pipe, looks unburnt on your finger.
And the compression may very well be low on #2 because the gunk around the exhaust valve is preventing a seal.
Two excellent points! Give the man a gold star. If the oil was coming from the rings it would be burned during combustion and the plugs would show it. The valve stem is heavily ladden with oily crust and the exhaust port is just as bad. The engine just never got hot enough in the open header mode because they were probably just short sprints and the oil exited really fast out of the engine and never got a chance to burn it like it did with the full headers and exhaust on.
Your next step will be removing the head, like it or not. This isn't some external fix where you force a can of DR. Good Stuff down the carb , and its fixed.