There is very little that changed strength wise in chev three speeds from 40-63, in fact the cluster gear stayed the same. Other changes did little to improve strength.
The most common failure is from lack of oil due to the common leaking problems torque tubes have both externally and internally back into the differential.
If your trans is in good shape to start with it will take some abuse.
Make sure the seal in the torque tube is also good.
