In my hunt for a set of good quality headers that work, I was given the name of FPA, Ford Powertrain Applications.  Stan Johnson there makes all the headers for Ford Racing.  My car is a '65 Fastback with a 351Stroker to 393cid.  I was having trouble with the Hooker long tube ones I already bought mounting to high on the cyl heads and creating problems hitting the floorboards.  I later found out the exhaust ports on the heads are 5/8 inch higher on the heads.  Anyway, Stan makes a set of headers for that engine in a '67 Mustang and he sent me a set to try.  The headers are truly a work of art, heavy 16 gauge metal with 3/8 flanges and already have the ball and socket mount-up on them.  They won't work on a '65 unless you have the shock towers reworked, but with my set-up. they worked perfectly.  Stan is a customer minded person and will listen to your questions instead of blowing you off like a lot of vendors do. He also makes headers for alot of other Ford applications and not only my motor.  His phone number is 253-848-9503 out of Oregon.  web page is www.fordpowertrain.com.  The price of the headers is reasonable plus they are beautiful and work.  He said I could refer anyone to him and he would be happy to talk to them about their project.  I am attaching some pictures of them and how my shock towers are reworked.  Hope this helps