Inner Fender Replacement

You don't state whether the damage occured on the right or left side of the vehicle. If the collision was on the left side check the gaps on the right side. If the collion was on the right etc...

If hit just right you can cause frame damage, and with speeds of 15 - 20 mph has an impact of 30 to 40 mph. Air bags are designed to deflate at about a 10 mph collision. A 10 mph collision can cause frame damage to unibody vehicles. A 73 Dart is a unibody vehicle.

Any damage that occured that caused an inner fender to buckle I would make sure the measurements are where they are supposed to be. But that's just me.