Do yourself a search of past threads on the subject of ex-racers,the subject has been done often enough.
As usuall I'll give you my opinion,but first a question.
1-What for you is the attraction of ex-racers as working dogs?
I can't see many advantages for having an ex-racer rather than a lurcher,the two that come to mind are,they are [mostly]free and they are aged to run[no waiting for them to age as you would if you bought a pup].
The best option is to buy yourself a well bred lurcher pup and train it up the way you want.If you get one some time soon it will be ready to start