1973 383 duster headers install

So your "No! No! No!" is everything I suggested except you'd rather also remove the radiator, steering shaft, driveshaft, drop the entire drivetrain along with the K-frame, AND disconnect the upper ball joints??
That sounds like a lot more than it is.
The only thing all that extra labor makes easier is getting some of the header flange bolts started... I have big hands and didn't have any problem bolting them back up with the engine in place.