If you really want to do this, you need to be smart about it. Take lots of measurements for starters. I would recommend removing the engine, and transmission, front suspension and use a bare empty K frame as part of your jig.
Now for a possible part of the problem. K frames are jig weld assembled in a fixture and are ALL of them exact at all 4 points so any 67-76 A body K frame will swap to any 67-76 A body. These are held on with shouldered bolts that locate it EXACT on 4 points. If your K frame is bent from the fender bender I would NOT use it to line up your new framerail. Your better off using a known straight K frame for that. The 2 shouldered K frame bolts, Theres your 2 points to get the rail square.
First thing you want to do go buy 4 magnetic spirit levels, remove your trunk carpet, and door sill plates, is get the car jacked and level on 4 points. Your concrete floor is not dead level. Put one spirit level on each rocker in the door opening, one in the trunk across the the transition pan above where the the shock bolts are, and one across the upper radiator support on the lip by the radiator top tank.
If your replacing the inner fender along with the framerail either temp weld or make and temporary bolt on supports from the firewall to the radiator support before removal to keep everything lined up. I recommend removing the inner fender from the replacement rail, then install the replacement rail, then install the inner fender second. Car in the pix has jack stands under the rear axle that are shimmed to make the bubble level in the back level from side to side. Jack stands in the front are shimmed with thin aluminum to make door opening rocker levels and radiator support levels well level.
The inner fender has alignment 5/16" holes at top front and top rear to line it up at the back and front. Use 5/16" diameter flat bottom punches to line them up before clamping and welding. Check every measurement multiple times before buzzing it together. Remember the whole car is nothing but alignment holes. Last pic if looking down through 1&1/4" hole in trunk floor. Corresponding hole at the bottom is a 1&1/4" hole the framerail. This is where this stuff was jigged together on a jig with steel pins and then workers pinched it together with spot welders at the factory. Remember they made 275,000 dodge darts in just 1969 this doesnt include the number of valiants and barracudas. This stuff had to have ways to fit it together quickly and accurately.
Hope this helps you out. Best of luck.
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