Give them a call and ask them "why". I used TTI headers in my 74 Duster with the supplied bolts. If I had studs in the heads it seems like it may have been difficult to get the headers passed the studs though probably not impossible.
FYI: My wife was nice enough to wrap each of the tubes with the supplied bubble wrap so the tubes didn't scratch during intallation. Also, make sure you have the car high enough! (I wasted a lot of time!)