Not sure on the pinion shaft diameters between the 4 and 6 cyls, but, the stock axle shafts can withstand 7100 to 7400 lb/ft of torque. Chromo upgraded shafts (~$250 /pr) can withstand 8300.
Hope this helps.


85 4Runner - With NEW Marlin 4.7 Gears!! It's a whole new beast!