Inner Fender Replacement -'72 Valiant

Check the end of the frame for damage. You may want to wrap a chain thru a hole and pull it forward to get some of the kink out, depends on how far back the impact is. If it is in front of the shock mount, probably not much to worry about.
Take off the fender and anything attached to the inner fender.
You will find spot welds on the back edge of the inner fender by the firewall, along the shock tower, bottom edge and rad support. They all need to be cut. Spot weld cutter, drill bits, die grinder, what ever you have. Clean up all the ragged edges, and flatten you donor edges before you put them in place.
sometimes it is easier to cut out along side the spot welds and get as much of the sheetmetal out of the way as possible to give you more room to work.

Assemble, tack weld a couple spots and test fit the fender, hood and bumper grill. Check for alignments. You may have to get it straightened on a frame machine if there are serious problems here, or it may just be a simple change in the tack welds. Once you're satisfied, weld and finish.

Good luck