They made the "flange" on the thrust bearing larger in 74 and later engines.
However, I have seen that they incorporated the larger machining on it much earlier than 74.
So many of the pre 74 engines can still run the larger thrust bearing with the larger flange.
You can put the smaller flange main on all of the engines, but you can't put the large flange thrust bearing on one that doesn't have the deeper machining for it...
Always check the flange area of the thrust bearing with your bearing to make sure that they are compatible...
This was to help reduce wear on the thrust faces by providing more surface area to distribute the load....
