Why not take a new manifold gasket and some 3/8 flat bar for your flange stock. Then you locate a local shop that has a water jet cutter. Have him cut the flat bar stock to the gasket, they can cut with in a few thousandths of an inch. Then go by your local muffler shop and purchase U-tubing to make your exhaust port flanges, you will already have all of the angles in the U-tubes to design your down pipes too. Then you will need three of for straight peaces 36” long for the straight runners, and last some 2 ½” for your collector. You can do all the tack welding while the engine is in the car so that you won’t have any issues or interference problems. Then remove header after all tack welding is done so that you can then set the header up for proper angles for the final welding. Now you have something that fits the car perfect without having to peace mill parts from different cars. On top of it all the header will look appropriate for the car helping the engine to perform far better than a peace mill exhaust...