No adapters, the headers were on it when I got the truck. In fact, the engine that was in it had Track 1's on it. The tubes are formed at the header flange and are not perfectly round, kinda flat on the header bolt sides. And yes, they are 2-1/8 'cause I had to replace the collectors (bolt on) 2 years ago after a race at a junk local track ripped them off.