Tips needed on buying and installing '71 Duster lower door hindge.

You could scribe around the old hinge - at least as a starting point. Kick panel will have to be removed to access a couple of the hinge bolts. Support the open door with a jack (a second set of hands would be a good idea), remove all the bolts and hinge. A box wrench will fit in areas a wratchet won't. Line up the new hinge with your scribed marks and install all the bolts leaving them just loose enough to make adjustments. You'll only tighten/loosen one bolt on each half of the hinge while you make adjustments.

The bolts on the door half of the hinge will allow you to adjust the lower part of the door in or out from the body. The bolts on the cowl half allows up and down, fore and aft. The upper hinge will prevent any vertical adjustment of the door and that's okay. It will still move fore and aft. If it's too far forward then the rear edge of the door will droop. Too far to the rear and the rear edge of the door will be too high when you try to close it. When the door is adjusted where you want it then tighten the rest of the bolts.

Just remember that a tiny adjustment at the hinge can translate to a large movement at the other end of the door. Loosening or removing the striker from the jamb may allow you to get the door squared in the opening easier for closing.

Also, hinge replacement may not be necessary. You can buy hinge repair kits with new pins and bushings at your local auto parts store. The springs are also available separately but harder to find. I would repair what you have before buying replacements (that someone else has already rebuilt). It's a lot cheaper.