Get Running & Driving 2-1965 Dodge Dart

So I've got all my brakes rebuilt. Waiting on a new dual master and brake line kit from In-Line Tube. I have a distribution block, supposedly correct for the conversion except it has 4 exit holes and I only need 2 for the front and one for the rears. The plug I have fits every hole except the one hole I need to plug. Anyone know what size that odd hole is? Pretty sure it's the one I'll need to plug or spend another $40 getting the correct block.
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