they were used about 82-92, and I've heard the later half were somewhat improved, but they're all the same gearing AFAIK .... for the rear you might investigate using a center section from a 55-59, I'm not sure if you need the axles as well, some of the AD series folks here could expand on that - you still need to weld up the 'pivots' on the torque tube rear, but it might make an easier change
Bill
