The old "657" carrier is one of the first 8-3/4 carriers and is equal in strength to a 741 carrier. The big problem is they were used in the old style rearend with press on brake hubs. A couple yrs. ago I got one and beat my friggin brains out with a 3lb. hammer trying to get those drums off (didn't have a torch).
The "657" carrier can be installed in any other 8-3/4 housing so look at it close and if it is the newer brake style (slip off drums) and the price is right it's worth having. If it is truly in an original A-body housing that means it was transplanted cause they stopped using the 657 carrier before the A-body 8-3/4 was made.