You might try Rick Cressi at Tri-C Engineering, located at 24927 Tibbitts, Valencia, CA 91355. The telephone number is (661) 295-1550. Rick has built a set of headers for my ERA, as well as a set for an original GT 40. I do not know whether he would be comfortable building a set of headers without the car, but he might be. He also does exceptional work, at a reasonable price.
Michael