If I were doing them for a living there's a plastic tubing kit where there's a ton of curves and straights that snap together and make each tube (all four at one time). They come in different size tubes and allow for any bend and really look like a header when all snaped together, infinitely adjustable. They start at $245 and go up, no more guessing and trial fitting.
Isn't that the kit that you send in to have the pipes bent to there shape?
Ice engine works
"Dramatically simplify header and turbo manifold design and fabrication with these modeling blocks from Icengineworks! These blocks simply snap together to form header primaries that can then be duplicated by cutting and welding commonly available prebent U-bends and J-bends.
Included with each kit are both straight and curved blocks in a variety of radii. Each block represents a 1 inch arc length of tubing. Blocks of different sizes can also be connected to simulate stepped headers. Each block is molded with a series of markings and index points to make the transition to metal as easy as possible."
