The big threaded plugs are used to delete an EGR pipe that runs from the exhaust manifold back into the intake (not on the earlier engines). Yes most of us will either cut up a block off plate out of alu or sheet metal but the fuel pump block off plate for a Ford or Chrysler can be used (AFAIK). You will also need to ensure the coolant port under the base of the carb is sealed up and the coolant barb where the water choke was hooked up to is sorted out (I removed mine and used a brass barb to reconnect the heater hoses).