This is far from an ATC push in theory. The big blind covers you by a lot, so the big blind is not that risk-averse against you, while you are somewhat risk-averse against the big blind. The Nash equilibrium pushing range here is 58%, not 100%.
In practice, you might be able to push ATC against a tight player in the big blind. You should be careful that the fact that the big blind has been tight so far does not mean he will continue to be tight. Many players are tight early, but open up a lot in the push/fold portion of the tournament. I expect that an unknown player with nitty stats in early levels will actually push quite widely from the small blind when the effective stack depth is up to 10 big blinds, and that he will not be surprised by a wide pushing range from you.
K4o is a lot better than 72o. You have more equity when you get called by hands like 22, 88, or A3. So, there are many times when it is not right to push 72o, but it should be profitable to push K4o. K4o is in the Nash pushing range, and I expect it would be a profitable push here.