When removing core plugs, I've always found you can make the plug rotate like a throttle valve by giving the very bottom (or top) of the plug a solid hit or two with a punch/hammer, then gently tapping it slowly to start it pivoting. Then grab the top lip sticking out with a pair of channel locks and use the natural shape of the channel locks as your fulcrum against the block (in fact, you don't usually need to even close the jaws on it, just hook the upper jaw into the core plug's upper lip and rock it out). Depending on clearance, you may want to decide which way you want to tap it. Whichever side you tap in, the opposite side will pivot out so if you have more room to yank the plug with the pliers sideways rather then straight up or down, then tap the left or right side in.