Below is from Moparts Tech Archive
Strength Considerations
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Pinions...
The 1-3/8" '741' pinion is the weakest. It is still a capable unit in most
moderate power, moderate traction street applications. For high torque
applications with high traction tires, the 1-3/4" or 1-7/8" should be
considered.
The 1-3/4" '742' has a larger rear pinion bearing yielding greater strength
in this area.
