what i have found from doing my own for so long is:
1. sometimes I can make a new one faster
2. when dealing with cracks and a maze of them sometimes it is better to cut on one side or the other and weld or braze from the back and front.
3. brazed ones will usually keep from cracking longer, but taking bends out by sealing the ends and heating them up is all but impossible. if the brazed section raises back up at all, it will generally leak badly.
4. if the header and cylinder junction is good, and the back cone is good, and I have a decent one to work off of I can get the length right and end up with the same performance that I began with.