Remove the rockers and check the push rods for #2 & #7 to rule out the push rods being bent or out of the lifters.Shine a light in through the opening in the heads and turn the motor and watch the lobes on those cylinders.If 2 cylinders have black fouled plugs there's a reason,cam lobes,push rods,or if you're running KB107 pistons the top ring gap was too tight and snapped the top off the pistons.Since you've checked the ignition look in those areas.