I did mine last year in my garage. '69 runner,383 4 speed manual steer and brakes. Front wheels on wooden blocks. Passenger side fell out and fell right into place. All I had to do was take the main motor mount bolt out and jack the engine up a couple inches.
Driver's side, unbolted motor mount, jacked engine up a few inches. Did not undo anything clutch related. Did remove starter. Old header came right out. New left header slipped almost into place, but needed a couple more inches for it to go all the way in. Fortunately I have a brick floor in my garage, and just pulled a few bricks out, and then it popped right in.
Got Flow Tech Ceramic headers thru Advanced Auto, 30-35% off, free shipping. The only problem I had, was the passenger side went so easy, I decided to do the driver's side. Having to fit the original Chrysler starter in place with the new header hanging there, I got tired, frustrated. But it was very easy to do, just make sure you have the car up high enough. I had a 4x8 and a 2x8 stacked under each front wheel.
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