The Mopar (Dodge/Chrysler/Plymouth) A-Body (Dart, Duster, Demon, Scamp, etc) engine compartment is rather small. A lot of the work to be done to an engine that is installed takes some tricky manuvering, or shifting the engine around.

Installing headers in an A-Body is a particularly complicated task.

Here's the sequence to follow to complete this task:

This is easier to do if you have at least one other person assisting you, from the top of the engine.

1. Disconnect battery.
2. Jack up the driver's side of the car, place a jack stand underneath the driver's side front.
3. Unbolt the motor mounts (both sides).
4. Place a block of wood on your floor jack, position the jack underneath the oil pan.
5. The passenger's side header should slide in from underneath without much of a problem. You might have to jack the motor up a bit to get it in, though.
6. Jack up the engine as far as it will go. You can remove the distributor cap to give you some added clearance. BE CAREFUL, the distributor will be pressing against the firewall at this point.
7. Take a break, have a beer.
8. Disconnect the center link from the steering box arm and driver's side tie-rod.
9. Have a buddy stand on the driver's side of the engine with a crow bar. Position the crow bar between the motor mount and the engine block.
10. As your buddy pushes the engine as far as he can towards the passenger side of the car, slide in the driver's side header from underneath the car.
11. Lower the engine down off the jack.
12. Take a break, have a beer. Offer your friend a beer.
13. Bolt the headers up to the engine.
14. Unbolt the headers, you forgot to install the gaskets.
15. Take a break, have a beer. Offer your friend another.
16. Bolt the headers up to the engine.
17. Put the steering linkage back together.
18. Bolt up the motor mounts.
19. Have the front end aligned.