Yeah, two diferent companies. Here is a short timeline regarding Doug's and Doug Thorley. Posted on HAMB.

"Actually here is the real scoop. The original company that Doug Thorley started was a muffler shop back in 1958 in East LA. In the early 60's Doug started to make headers and "Headers by Doug" stickers started showing up on winning drag cars. Doug and wife Betty sold the company and got divorced and new owner Micky called it Doug Thorley Headers. A number of years went by and Micky got sick and asked for help. Betty came back in to run things and Micky got worse. He ended up selling the company back to Betty, Doug and a third partner. Doug mainly did R&D and was an investor. Eventually He and Betty had another falling out and she agreed to buy him out. Doug kind of stayed away at this time, occasionally coming around to help out with a little R&D and collect his payments. Betty then got sick and at this time Doug started doing custom headers again under the Doug's Headers name. During this time Doug Thorley Headers was mainly making truck and motor home headers, not muscle car or performance parts. Betty passed and Doug started making production headers again for the classic and muscle car markets. After about another year, the surviving partner sold Doug Thorley Headers to Summit Industries (not the mail order guys) in Corona, Ca who previously had bought out Jerry Jardine of Jardine Headers.
PerTronix, who had previously acquired Ermie Immerso Ind and Thunderbird Headers bought Doug's Headers and Doug worked to help keep the Doug's Headers line a top quality product. PerTronix sells and manufactures them as a premium line to compliment their Patriot Header line. They are currently made in Rancho Dominguez (think north Long Beach) CA.
Doug was also famous for his drag cars - The Chevy II Much that is in the NHRA museum, the Funny Car Corviar that Joe Piasano ended up with, and the pair of rear/mid engined Javelin's."