I had a 64 Barracuda with a 1/2 filled 340 block and an extra capacity oil pan. I had fenderwell headers so lots of underhood heat. I cut the core support and mounted a wide aluminum radiator but the issue was really not enough space for air to get out of the engine compartment. I ended up using a hole saw to put some holes in the inner fender to let air out. I dont remeber how many holes I ended up with behind the shock absorber area and under the fenderwell headers but it looked like swiss cheese before I got enough air out to keep things from roasting under the hood. I also removed the plastic plugs up in the cowl area. The guy who bought the car from me didn't like the look of the holes so he cut the area out and welded in sheet metal. He quickly found out why those holes were there and his new metal work got even larger holes!