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I once knew the answer, but I don't think 35 spline is common in OE and Superduties shouldn't have 28 spline axles either. That should leave only 31 spine left. However I am not certain. Unless someone knows for sure, then the only way to check is to pull the axle and count the splines, or you might be able to count them if you pull the cover.
This Hennessey Takes the Expedition Tremor's Off-Roading Capability to the Next Level
Slideshow: The VelociRaptor Expedition gains a lift, upgraded suspension, Brembo brakes, and trail-ready equipment while retaining the stock 440-horsepower EcoBoost V6.
Rezvani's Latest Post-Apocalyptic Monster Is a Ford F-150 Raptor Underneath
Slideshow: Called the Fortress, the 850-horsepower pickup combines Raptor underpinnings with military-inspired features, survival equipment, and a starting price of $285,000.