I've done this job before, first off if you look at the picture Trevor provided in the link you will see the the frame rail curature is the section of frame rail from the the crossmember back, the front frame horns are a add-on piece that comes from the fornt crossmember forward and can be bought new like that. if you cut the old ones nice, neat and square, then the new horns will weld on at the appropriate curvature, because that is being set by frame rails and the angle of the front crossmember. Also their is a front lower control arm mounting brcket assocaited with this job,and you may need to replace it as well on each size. This stuff, even the stock stuff isn't made from much, more or less folded over sheet metal, I even seen folks make the front frame horns from sqaure tubing from stratch, another possiblity, it is a easy enough piece for a average fabricator to make. Also so while you are doing this job, if this is not a 1500 car, you'll have a steering rack crossmeber that is full height across the the fornt of the engine and makes access to the nut on the front of the crank balnacer impossible to get to, on our race cars, we cut the middle of the is steering rack cross member out and make downward bracing to front cross member that leaves a access area to get a 1 5/16" socket on the front crank balancer bolt, which makes turning over the engine by hand for jobs like valve adjustment so much easier, the factory should have already did this, but the front frame horn replacment job is excellent time to look into doing this as well. Hope this helps.