8 3/4 question
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 1-7/8" '489' is supposedly the strongest. Although the stem tapers down
along it's length, it appears inherently stronger from a pinion stem
perspective and the inherent strength of the fine splines (OEM gears).
The 1-3/4" '742' has a larger rear pinion bearing yielding greater strength
in this area. The 1-3/4" shares yoke mount diameter and mounting nut
with the 1-3/8".