If the radiator is mounted on the chassis, a core support is useless. It serves no purpose other than to be heavy. All you need is some tubing to hold the fenders together and a bit of a lower frame to mount the nose to the car.

If you look at Jerry's pic, the stock core support he has left could easily be done from round tubing, mount right at the front of new rails and is likely less work. Unless you just WANT a factory looking support, which some do