|The three types of mainshafts are early dry clutch (left), early electric start (middle), and late wet clutch (right).
The two early shafts have a hole through them lengthwise to pass the dry clutch release rod. The late shaft is solid, the wet clutch release is in the primary cover.
The mainshaft bearing race was the same part from 1952 to 1983. In early 1984 it changed, and then changed again in late 1984 with the clutchernator. That later part is not covered here.
The mainshaft bearing race goes on the far side of these shafts. It is pressed into the case. If you replace it, you should hone the bearing race before running the tranny.