If you're having trouble getting the bolts off the frame, there are 2 tried and true ways to do it. First, use penetrating oil and keep squirting them for a few days before attempting to loosen. The worst thing you can do is round off the bolts or nuts. Second method is heat- not propane Bernz-a-matic heat, but an oxy/acetelene torch kit. Heat 'em cherry red, then try to unbolt them. Last resort you'd use the torch to cut them off by melting away the nut.
You can use these methods on the bumper itself-with caution if you're trying to save the bumper- but the bumper bolts have a square flat at the base of the head that actually tightens the bumper to the bracket. You must be careful again not to round off the square flats or the bolt will keep spinning. You need to keep tension on them from the bracket side of the bolt by using a prybar, screwdriver or something to wedge between the bracket and bumper. All the sloppiness must be taken out or rounding will result.
Clean off all the threads of each bolt with a wire brush before starting any of the above to make it easier for the nut to run down the threads.
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