Depends on what you want to do with the car. My 67 390 has an open 3.00 and it's hard to keep it straight under hard acceleration. It's scary to think what it would do with a trac-lock.
If you have to take it apart anyway, sure. But to do it just so you can say "I have a trac-lock". Save your money. Of course, if your going to the track, well that's different..
just my opinion..