The 70-71 tracks had a double lock setup meaning both the inside and outside tracks locked requiring a cable from the release handle on the outside track to connect to the inside track.
The 72 + had a single lock on the handle side track. The bearing guides on 70-71 were metal and 72 + plus were nylon. These sets are all interchangeable for any model year.
I believe the 72 + were a better design.
Slotts
