After a quick and frustrating/disappointing phone call with The Driveshaft Shop, I have decided to cut my losses and throw their whole driveshaft setup in the garbage and go a different direction.
Huge thanks to D&D for the quick hookup on parts and Capizzi for doing the install on such quick notice. Also D&R for the driveshaft. It's now converted to a Magnum T56 slip yoke style setup. Was a fun ordeal to install since the u-joint is larger than the old driveshaft diameter and I had to move the engine/trans to the side to clear the suspension crossmember.
This little part was the biggest road block to the whole conversion. Tremec shipped the wrong part in the right packaging and I spent a whole day driving all over the state to track one down.
Fixing the header adapters the right way since I had more time.