I ordered the captive nuts from one of the parts houses. It came as a kit with the bolts (leaf spring front eye bracket kit). The captive nut brackets have an angle to them that slip into the elongated, rectangular holes in the frame rail just above where the bolt goes through on the inside hole and the floor pan on the outside and front. Do not over tighten these as the captive nut tends to break away from the bracket. If this has already happened with the bolts you have remaining, you will need to grind the heads off to remove the eye brackets. As Rick said, carefully cut the weld holding the eye bracket to the frame rail.