Ford f150 rear pinion spline
 

To start I'm working on my 2002 f150 5.4l V8 4x4 with 9.75 limited slip differential with 3.55 gear ratio. Recently I wanted to change my ratio to 4.10 ring and pinion and have unsuccessfully found a reliable source for the pinion spline count. Everything says 34 spline count but those gears are very rare and 31 spline seems to be the most popular and the spline flanges I found are 31. Any help would be great