Okay, I would like Andy F's opinion on this as well but according to Chuck Senatore's "Big Block Mopar Performance" filling past the top of the core plugs in a big block Mopar will block the coolant flow past the first set of head bolt bosses in the cylinder bank and "make an even heavier boat anchor" but I don't know if this applies to 9.98 inch deck B engine only or to 10.72 inch deck RB engine as well. You may want to shine a bright LED light into your lower water pump holes and make sure you can see light shining into the rear of the water jacket through the coolant holes in the rear of the deck.
