More Header Questions

I misplaced the cam card,but I know it is a custum ground bullet 600 lift,108 CL.Motor was built and dynoed by RyanJ.primary tubes are 35''collector is 4 into 1, 3'' diameter style 12'' long to bolt flange then a12'' extension.Sad to say He said it made 560 HP.with 1.7/8 shoefield dyno headers.He told me to try the smaller header first.Motor peaked at 6200,6400 then dropped off,have tried shifting the car at 6200 doesn't go faster shifting higher.