On 235's there is a spacer that keeps the gear from being pushed on to far. In affect it sets the clearance between the gear, thrust plate and cam.
The spacer is not essential but it makes it easier to assemble. The earlier Chev's did not use the spacer, you just used a feeler gauge to set the thrust plate clearance when pressing the gear on.
If you want to use a spacer and can't find one PM me.
