Hedman Headers 78500

ISO Hedman Headers 78500. I am wanting to try these on a 1964 Plymouth Barracuda w/318, no power steering. I know they are not listed to fit this model, but I am currently running 1968 340 manifolds w/o any issues (but an exhaust leak at the flange...). Any assistance, thoughts, comment, concerns, etc, etc... Let me know if anyone has anything. Thanks.