I spent some time modeling this in Fusion 360 and can show here if you cut the axle end at 20* and use Carlisle Turf Masters 13X6.50-6 and Douglas 6" wheels with and offset of 6.5'' x 2.5' and a 4" x 5/8" spindle that will produce a scrub radius of 2.5" I would go with less scrub radius but I'm maxing out the mechanical capabilities of the heim joint. I'll set caster at 12*.
In short, 20* KPI, 12* caster, 2* toe-in and 2* camber. (weld spindle with static or fixed camber)
If you don't do this and put front brakes on your axle then every time you apply breaking force the wheel with the most traction will force your steering wheel to turn the opposite because of the rotational force. The negative camber will give the added benefit of providing more grip in the turns while sacrificing some on the straights. Like I said, when you're on turf or grass and going in circles it's less effective to have a large scrub radius with no camber as George has suggested. Less scrub radius and a few degrees of camber is good, even with bias ply tires. Might also be a reason why George had to shift his weight so much like he talks about when he was racing and taking corners.
Here's a CAD drawing of it to illustrate what I'm saying.