You have TTIs, Dougs, or Spitfires.
TTIs are the most complete. PITA to install, but they are the most complete long tube header.
Doug's are the original. There's one (or 2, can't remember, been awhile since I had my early A info) slip fits. Definitely pricy, and don't require AS much work as the TTIs to put in, but still a PITA
Spitfires. Well there's a hit or miss brand. I've ordered 2 sets of these, and got them on time as promised. Many others not so lucky. $175 for the sets 4 years ago. Layson's sell these also for $400 a set? either way, what you save up front, you'll pay with a coating and welding on your own down tubes. Drivers side will be a PITA to fabricate.
I'd go with TTIs as well. Sure as heck more $$$ up front, but probably the best choice of the 3 major brands.