On one side, the internal threads were gone and the bumper bracket was welded on and on the other side, the threads were rusted out. Here is how I fixed the mounts.
First measure from existing mount holes to another point on the frame for later reference. Mark a vertical line a little past the mounting holes and cut just the outer metal of the frame rail. Mine was not terribly rusted out so I cut only about 8 inches back just for replacing the threaded holes.
Next drill out the spot welds around the front edges of the rail. I actually ended up cutting a couple of the bottom ones with a disc. Remove the old piece.
Clean up the rust and prime.
Measure, mark, cut the new front out frame rail piece to fit the space. On mine I drilled holes for plug welds. Verify that the hole measurements are what they were before and clamp and weld in place.
Since I had a lot of metal left after cutting the rail patch to fit, I used the rest to make the patch for the other side. I took measurements and drilled holes to match the old metal. I welded in a couple nuts and cut it to match the old piece. I also needed to add the tabbed piece on the end that the lower valance and bumper guards bolt to.
Next I started working on the body pieces for the nose. This was the headlight buckets, lower grille support, stone deflector, and headlight doors. I had 2 pairs of buckets to choose from but only 1 pair of doors so I picked the ones that fit the doors the best. Starting with 320 grit, I sanded the old paint, primer and scratches. Next came the high-fill primer coats. The stone deflector had some deep gouges from someone's attempt at removing old paint so I skimmed on some 2 part icing.
For the buckets and headlight doors, I just used some of the spot putty for scratches and pits. I sanded smooth and repeated the high-fill and a couple touches of spot fill followed by some wet sanding with finer paper and another coat of high-fill and more wet sanding.
After some test fitting, I found that my cheap e-bay shelby style valance will take a lot of persuading to get it to line up (must be why they were trying to offload it for cheap). You have to drill all your own holes on this so it took some time to complete.
I needed a good top coat for the rough hot rod phase. It'l be a while before real paint goes on and I plan to drive it ;)
I experimented a little and came up with a buffed primer finish that looks a little like the dull black paint that some people like these days. Its just a black wash-primer lightly buffed after it dried.
All assembled with its new grille, its starting to look road-ready.