What about the other bolts that pass through the fender well and into the engine bay? Are they tight? Do they have washers? That longer drop arm increases the stress on a frame that it was not designed for. Have you removed the bracket entirely and checked for a cracked frame? This is not uncommon. The fix is to tie both frame rails together at the track bar bracket (after welding up the frame rail). There are product available for this issue (Track bar brace).

Its pretty obvious from the photos that the only part of the bracket making contact with the frame is the area directly under the bolt. Adding washers is a must as suggested above. Keep in mind that bolts are weakest to shearing forces. That is what these two bolts are subjected too. The more you spread out the load by using washers and or backing plates, increases the holding power of these bolts. You want as much contact as possible between the bracket and the frame.

Since the holes are hogged out already, you should drill them out to the next size up. Make the holes as tight fitting as possible and using washers on both sides to spread out the load. Throwing new parts at this problem may not fix it. Make sure everything is correct first, then if you want to spend money and upgrade you can be sure you didn't waste your money.