I have the TTI 2.25" primary 4" collector headers on my '70 cuda. It has all stock front suspension and everything else.
The passenger side header will go in the car after the motor is in. If you unbolt it, it will just about fall out of the car. Bolts aren't that bad to do from underneath the car. Had to do a little massaging to the top outer primary tube to clear the torsion bar ahead of the collector.
The driver's side Needs to be in the car prior to the motor going in. Most of those bolts are easily done from up top.
I do have a motorplate instead of factory mounts.