I think they choose me!
They just seem to appear and I feel sorry for them and have to help them!
Without it in you hands you really don't know or rather can't tell if it is savable. It all depends on how much damage has been done by the original builder as to what to do with one.
Some maybe are a subject that you might want to put back original if possible. Others is there is too much missing and too parts hard to find you might say "custom" or "hot rod" or maybe dirt track car, etc.
I don't know if there is really a standard answer to that question. Guess it is all in the eye of the beholder or even based on a builders abilities.
I know sometimes you lose one after tying into it and finding it's too far gone or as I had happen recently just mess up!