had trouble w/reds and some i just got from speed way, they fit the block great but if you take a light and look in them you will see that the hole in the intersection of the pipe is only about 3/4 inch around, would choke the eng. took a stick welder and turned up the power and stuck the rod in and burned out the hole, careful not to blow hole in header. mine were belond center dump style. don't kno how you would fix the swept back type. when i have made headers i scribed the intersecting pipe and cut out to fit w/max hole, then weld,they just blow a hole w/torch and weld.