[PGSigns]

We ran mud bog trucks for several years with 12 bolts and never broke a pinion. We broke a bunch of gears and twisted some splines but never a pinion. None of the truck 12 bolt is cast iron but the center is cast steel. We have welded the tubes to the center a couple of times no issues with proper welding procedures. So no issues with welding. Now gears come in different flavors. You can get drag race gears, off road and street gears and the low price gears. So application drives the gear material. So a well built 12 bolt will serve you well, but with your plans to drag race, auto cross and street drive I would build a 9". Then there is the suspension ad how you decide to do that as all three of your choices can drive 3 different suspension setups. A good auto cross setup will not make a good drag race one.
Jimmy