I gave up TTI distributorship 2008ish cuza the rust issues, trying to deal across the border was a major pain, - started installing Dougs .
Slip joint was original design, they changed to a design very similar to Doug's, over linkage, no slip-joint.
I ran Dougs on my 65 360 Valiant back in the mid 90s. Those were the easiest installing headers ever. They fit fantastic. I wish they'd make some slant 6 headers.