2&1/8" tti in 73 duster

Buck - I would massage. Those are some very big headers and they work well. I used Schumackers, they work well but you will take a hit on the power on that beast. I then went to the same TTI's and it made a world of difference. #6 was a problem with plugs, so I drilled a hole.

Make sure your engine is level and square in the compartment, may lead to other issues such as heat, fan space, or binding in transmission.

Good luck - 766 is a lot of motor for an A-Body, assuming you have a torque strap and frame rails?