Oh whoops, LOL. Sorry, I completely missed ay the end where you said you're making a new axle.
I think for an all around off-roader 0° of camber is what most guys do, but for an actual track racer it might be different. I've never done that type of thing before so unfortunately I couldn't give you a number.
For just a general off-road tractor though I would say 0° of camber, and maybe 7° - 10° of positve caster would go a long way in the handling department.