My buddie had a 67 Fury State Police ex squad car with a 440. It had 5/16" fuel lines. I was the guy that changed the rotted through steel fuel lines on all the old cars back then at the gas station I worked at. I change a boat load of those 5/16" lines that ran through the frames on the old C body cars up through the mid 70s. I had a system down I could change the steel line in about 10 minuets once the dirt was cleaned of the frames. Gene